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排序方式: 共有300条查询结果,搜索用时 31 毫秒
221.
Extremely low density InAs quantum dots (QDs) are grown by molecular beam droplet epitaxy. The gallium deposition amount is optimized to saturate exactly the excess arsenic atoms present on the GaAs substrate surface during growth, and low density InAs/GaAs QDs (4× 10^6 cm^-2) are formed by depositing 0.65 monolayers (MLs) of indium. This is much less than the critical deposition thickness (1.7 ML), which is necessary to form InAs/GaAs QDs with the conventional Stranski-Krastanov growth mode. The narrow photoluminescence linewidth of about 24 meV is insensitive to cryostat temperatures from IO K to 250K. All measurements indicate that there is no wetting layer connecting the QDs. 相似文献
222.
We propose a novel scheme to trap cold polar molecules on the surface of an insulating substrate (i.e. a chip) by using an inhomogeneous electrostatic field, which is generated by the combination of a circular charged wire (a ring electrode) and a grounded metal plate. The spatial distributions of the electrostatic field from the above charged wire layout and its Stark potentials for CO molecules are calculated. Our study shows that when the voltage applied to the wire is U = 15 kV, a ring radius is R = 5 mm, the thickness of the insulating substrate is b = 5 mm, and a wire radius is r = 1mm, the maximum efficient trapping potential (i.e., as equivalent temperature) for CO molecules is greater than 141.7mK, which is high enough to trap cold polar molecules with a temperature of 50 mK in the low-field-seeking states. 相似文献
223.
The electronic structures and absorption spectra for both the perfect PbWO4 (PWO) crystal and the three types of PWO crystals, containing VPb2−, VO2+ and a pair of VPb2−-VO2+, respectively, have been calculated using CASTEP codes with the lattice structure optimized. The calculated absorption spectra indicate that the perfect PWO crystal does not occur absorption band in the visible and near-ultraviolet region. The absorption spectra of the PWO crystal containing VPb2− exhibit seven peaks located at 1.72 eV (720 nm), 2.16 eV (570 nm), 2.81 eV (440 nm), 3.01 eV (410 nm), 3.36 eV (365 nm), 3.70 eV (335 nm) and 4.0 eV (310 nm), respectively. The absorption spectra of the PWO crystal containing VO2+ occur two peaks located at 370 nm and 420 nm. The PWO crystal containing a pair of VPb2−-VO2+ does not occur absorption band in the visible and near-ultraviolet region. This leads to the conclusions that the 370 and 420 nm absorption bands are related to the existence of both VPb2− and VO2+ in the PWO crystal and the other absorption bands are related to the existence of the VPb2− in the PWO crystal. The existence of the pair of VPb2−-VO2+ has no visible effects on the optical properties. The calculated polarized optical properties are well consistent with the experimental results. 相似文献
224.
Yih-Pey Yang 《Journal of luminescence》2007,127(1):186-191
The effectiveness of a substitute of natural lung surfactants on replacement therapy strongly depends on the stability of the monolayer of those substitute molecules. An atomic force microscope is utilized to investigate the microstructure of the films of the major components of natural lung surfactants, dipalmitoyl phosphatidylcholine—DPPC, which are transferred to mica substrates by the Langmuir-Blodgett film technique. A concave deformation structure was first observed for DPPC in solid phase. The depth of the concave domain was about 6 nm and was remarkably uniform. For a collapsed DPPC monolayer, the surface film consists of a granular convex multilayer structure and a disc-like concave structure. Dynamic cyclic compression-expansion experiments indicate that the formation of the concave domain is a reversible process while the process for convex multilayer formation is irreversible. This gives direct evidence that convex grain is the collapsed structure of DPPC monolayer and the concave shallow disc corresponds to the elastic deformation of a DPPC solid film. Results of atomic force microscopy indicate that the nucleation and growth model instead of the fracture model can better describe the collapse behavior of a DPPC monolayer. 相似文献
225.
The ion flux dependence of the self-organized Si nanodots induced by 1.5 keV Ar+ ion sputter erosion has been studied. It shows that for the regime with ion flux >∼280 μA/cm2, the currently adopted Bradley-Harper (BH) model, which is incorporated in a dynamic continuum equation holds valid. However, for ion flux <∼280 μA/cm2, the measured dot size and surface roughness deviate drastically from the BH model. To interpret the data for this lower ion flux regime, the effect of the Ehrlich-Schwoebel (ES) step-edge barrier was introduced into the continuum equation. A consistency between the calculated and the experimental results was reached, furthermore, a reasonable trend was found, that is, the effective ES diffusion decreases steadily with the increasing ion flux, and at ∼280 μA/cm2, it became negligibly small. 相似文献
226.
Piezoelectric evaluation of ion beam etched Pb(Zr,Ti)O3 thin films by piezoresponse force microscopy
The evolution of piezoelectric properties of Pb(Zr,Ti)O3 (PZT) thin films after ion beam etching have been investigated at the nanoscale level by piezoelectric force microscopy. A comparison of the piezoelectric properties on etched and unetched films is realized. Piezoelectric contrasts imaging evidences a modification of the domain architecture at the film surface. Local piezoelectric hysteresis loops measurements on grains indicate that the coercive voltage for switching is much higher for the etched films (2.3 V) compared to the unetched ones (1.0 V) while the average piezoelectric activity is slightly lower. The results are explained in terms of grain-damaging during etching and domain-wall pinning. 相似文献
227.
The electronic structures and absorption spectra for the perfect PbWO4 (PWO) crystal and the crystal containing lead vacancy have been calculated using density functional theory code CASTEP with the lattice structure optimized. The calculated absorption spectra of the PWO crystal containing exhibit seven absorption bands peaking at 1.72 eV (720 nm), 2.16 eV (570 nm), 2.81 eV (440 nm), 3.01 eV (410 nm), 3.36 eV (365 nm), 3.70 eV (335 nm) and 4.0 eV (310 nm), which are very close to the experimental values. It predicts that the 330, 360, 420, 500-750 nm absorption bands are related to the existence of in the PWO crystal. 相似文献
228.
H. R. Zeng K. Shimamura E. A. G. Villora S. Takekawa K. Kitamura J. Y. Xu Q. R. Yin 《固体物理学:研究快报》2007,1(2):R62-R64
Ferroelectric domain structures of (001)‐oriented Pb(Zn1/3Nb2/3)O3–7%PbTiO3 (PZN‐7%PT) single crystals were visualized and characterized by piezoresponse force microscopy (PFM). Locally regular domain configurations are found to be possibly related to the stable macroscopic properties in the PZN‐7%PT single crystals. Nanoscale piezoresponse hysteresis loops measured by PFM tip revealed no evidence of local domain switching behavior in the PZN‐7%PT single crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
229.
Jan Čermák Bohuslav Rezek Věra Cimrová Drahomír Výprachtický Martin Ledinský Tomáš Mates Antonín Fejfar Jan Kočka 《固体物理学:研究快报》2007,1(5):193-195
Thin hetero‐junction composite films of polymer (electron donor) and fullerene (electron acceptor) are prepared on indium‐tin‐oxide coated glass by spin‐coating from solution in dichlorobenzene. Optimized atomic force microscopy (AFM) parameters allowed us to scan these soft composite films in contact mode and to measure their local conductivity with high lateral resolution by current‐sensing AFM. The morphology and local conductivity data are correlated with Kelvin force microscopy and micro‐Raman mapping and discussed with view to their photovoltaic properties. Regions with both compounds present are compared to areas where the components segregated, acting as shunts of the junction. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
230.
Jung‐Bin Yun Sejin Kim Sunae Seo Myoung‐Jae Lee Dong‐Chul Kim Seung‐Eon Ahn Yongsoo Park Jiyoung Kim Hyunjung Shin 《固体物理学:研究快报》2007,1(6):280-282
Resistive memory switching devices based on transition metal oxides are now emerging as a candidate for nonvolatile memories. To visualize nano‐sized (10 nm to 30 nm in diameter) conducting filamentary paths in the surface of NiO thin films during repetitive switching, current sensing–atomic force microscopy and ultra‐thin (<5 nm) Pt films as top electrodes were used. Some areas (or spots), which were assumed to be the beginning of the conducting filaments, appeared (formation) and disappeared (rupture) in a localized and random fashion during the switching and are thought to contribute to resistive memory switching. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献