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21.
Swarup Kumar Maji Anup Mondal Bibhutosh Adhikary Basudeb Karmakar 《Journal of Physics and Chemistry of Solids》2011,72(6):784-788
We report the formation of mesoporous zinc sulphide, composed by the fine network of nanoparticles, which was formed via a single precursor Zn(SOCCH3)2Lut2 complex. The complex was chemically synthesized using zinc carbonate basic, 3,5-lutidine and thioacetic acid, in air. The metal precursor complex was characterized using different conventional techniques. Thermogravimetric analysis (TGA) result indicates that the decomposition of the complex starts at 100 °C and continues up to 450 °C, finally yielding ZnS. ZnS nanocrystals were characterized by powder X-ray diffraction (XRD) technique, field emission scanning electron microscopy (FESEM), N2-sorption isotherm, UV-vis spectroscopy and photoluminescence (PL) spectroscopy. The grain diameter of nanocrystals was found to be 4-5 nm. The material followed Type-IV N2-sorption isotherm, which is the characteristic of mesoporous materials. The band gap energy, as obtained from optical measurements was around 3.8 eV. 相似文献
22.
In this study, in situ control growth of bismuth nanoparticles (Bi0 NPs) was demonstrated in bismuth-based glass dielectrics under an electron beam (EB) irradiation at room temperature. The
effects of EB irradiation were investigated in situ using transmission electron microscopy (TEM), selected-area electron diffraction
and high-resolution transmission electron microscopy. The EB irradiation for 2–8 min enhanced the construction of bismuth
nanoparticles with a rhombohedral structure and diameter of 4–9 nm. The average particle size was found to increase with the
irradiation time. Bismuth metal has a melting point of 271 °C and this low melting temperature makes easy the progress of
energy induced structural changes during in situ TEM observations. This is a very useful technique in nano-patterning for
integrated optics and other applications. 相似文献
23.
F. C. Jain B. Miller E. Suarez P.-Y. Chan S. Karmakar F. Al-Amoody M. Gogna J. Chandy E. Heller 《Journal of Electronic Materials》2011,40(8):1717-1726
This paper presents the implementation of a novel InGaAs field-effect transistor (FET), using a ZnSe-ZnS-ZnMgS-ZnS stacked
gate insulator, in a spatial wavefunction-switched (SWS) structural configuration. Unlike conventional FETs, SWS devices comprise
two or more asymmetric coupled quantum wells (QWs). This feature enables carrier transfer vertically from one quantum well
to another or laterally to the wells of adjacent SWS-FET devices by manipulation of the gate voltages (V
g). Observation of an extra peak (near both accumulation and inversion regions) in the capacitance–voltage data in an InGaAs-AlInAs
two-quantum-well SWS structure is presented as evidence of spatial switching. The peaks are attributed to the appearance of
carriers first in the lower well and subsequently their transfer to the upper well as the gate voltage is increased. The electrical
characteristics of a fabricated SWS InGaAs FET are also presented along with simulations of capacitance–voltage (C–V) behavior, showing the effect of wavefunction switching between wells. Finally, logic operations involving simultaneous processing
of multiple bits in a device, using coded spatial location of carriers in quantum well channels, are also described. 相似文献
24.
A dual polarized aperture coupled circular patch antenna using a C-shaped coupling slot 总被引:1,自引:0,他引:1
Padhi S.K. Karmakar N.C. Sr. Law C.L. Aditya S. Sr. 《Antennas and Propagation, IEEE Transactions on》2003,51(12):3295-3298
The design and development of a dual linearly polarized aperture coupled circular microstrip patch antenna at C-band are presented. The antenna uses a novel configuration of symmetric and asymmetric coupling slots. Variations in isolation between orthogonal feedlines and antenna axial ratio with the position of coupling slots are studied and broadband isolation and axial ratio are achieved. The prototype antenna yields 7.6 dBi peak gain, 70/spl deg/ 3-dB beam width, 25 dB cross-polarization levels and an isolation better than 28 dB between the two ports. With an external quadrature hybrid coupler connected to the two orthogonal feedlines, the antenna yields 3-dB axial ratio bandwidth of more than 30% at 5.8 GHz. 相似文献
25.
P. K. Karmakar R. Bera G. Tarafdar A. Maitra A. K. Sen 《International Journal of Infrared and Millimeter Waves》1991,12(11):1333-1348
Rain, perhaps, is the worst offender for utilising Millimeterwaves in practice. This paper describes the rain rate distribution from which millimeterwave attenuation distribution have been attempted. Results reveal that in our location (Calcutta: lat 23°N long 88.5°E) the rain rate distribution fits well with normal distribution. The cumulative distribution of rain rate also prompted the present authors to find out rain attenuation cumulative distribution for both terrestrial and earth-space paths in millimeterwave band. 相似文献
26.
Like liquid alkali metalsd-shell liquid metals show scaling behaviour in structure and interaction potentials. A realistic interaction potential model,
properly parametrized can reasonably describe the universality in the isothermal compressibility and vacancy formation energy
of 3d-liquid metals in electron ion plasma model. 相似文献
27.
The average effective pair potential energy function between two neighbouring molecules has been computed from the centre structure factor data of water and this shows an unusual feature at short range due to strong hydrogen bonding. The effective potential is highly temperature dependent and at elevated temperature it turns out to be approximately like that for simple liquids. The effective potential can be represented satisfactorily by the square well model. 相似文献
28.
P.-Y. Chan M. Gogna E. Suarez S. Karmakar F. Al-Amoody B. I. Miller F. C. Jain 《Journal of Electronic Materials》2011,40(8):1685-1688
This paper reports the successful use of ZnSe/ZnS/ZnMgS/ZnS/ZnSe as a gate insulator stack for an InGaAs-based metal–oxide–semiconductor
(MOS) device, and demonstrates the threshold voltage shift required in nonvolatile memory devices using a floating gate quantum
dot layer. An InGaAs-based nonvolatile memory MOS device was fabricated using a high-κ II–VI tunnel insulator stack and self-assembled GeO
x
-cladded Ge quantum dots as the charge storage units. A Si3N4 layer was used as the control gate insulator. Capacitance–voltage data showed that, after applying a positive voltage to
the gate of a MOS device, charges were being stored in the quantum dots. This was shown by the shift in the flat-band/threshold
voltage, simulating the write process of a nonvolatile memory device. 相似文献
29.
Chen Sun Hirata A. Ohira T. Karmakar N.C. 《Antennas and Propagation, IEEE Transactions on》2004,52(7):1819-1832
A low-power consumption, small-size smart antenna, named electronically steerable parasitic array radiator (ESPAR), has been designed. Beamforming is achieved by tuning the load reactances at parasitic elements surrounding the active central element. A fast beamforming algorithm based on simultaneous perturbation stochastic approximation with a maximum cross correlation coefficient criterion is proposed. The simulation and experimental results validate the algorithm. In an environment where the signal-to-interference-ratio is 0 dB, the algorithm converges within 50 iterations and achieves an output signal-to-interference-plus-noise-ratio of 10 dB. With the fast beamforming ability and its low-power consumption attribute, the ESPAR antenna makes the mass deployment of smart antenna technologies practical. 相似文献
30.
A. K. Sen R. Bera P. K. Karmakar 《International Journal of Infrared and Millimeter Waves》1997,18(11):2233-2257
The use of Ka Band (20/30 GHz) for future satellite communications has been addressed. The exploitation of Ka band with a
bandwidth of 2500 MHz seems to represent the largest significant achievement in satellite communications potential, so far.
The problems associated with the use of this frequency band such as attenuation and receiver noise temperature (floor) variation
with rain has been addressed. The receiver noise floor variation with rain has so far been ignored. Therefore, in view of
propagation and noise study over this Ka Band, both signal attenuation and receiver noise floor variations with rain rate
are estimated using dual frequency radiometers operating at 22.235 and 31.4 GHz over a tropical station, Calcutta, India. 相似文献