共查询到10条相似文献,搜索用时 93 毫秒
1.
We report a luminescence study of the electronic properties of the 2D electron-hole liquid in crystalline Si quantum wells with SiO2 dielectric barriers. The Fermi-Dirac condensation of e-h pairs into a metallic liquid is strongly enhanced by spatial localization. We present experimental evidence for the formation of liquid nanodroplets, with size increasing with e-h pair density. The quantum confined regime is observed for well width below 15 nm. The data are analyzed in a confinement model that takes account of the band-gap renormalization by 2D many-body effects and the increase of the Coulomb interactions due to the dielectric mismatch between the Si well and the SiO2 barriers. 相似文献
2.
《Comptes Rendus de l''Academie des Sciences Series IV Physics》2000,1(7):911-927
For nowadays CMOS technologies, the gate oxide thickness has reached a few nanometer range and will be lower than 2 nm for sub-0.1 μ m generations. This scaling of the gate dielectric thickness favors the onset of physical phenomena such as gate polysilicon depletion or quantum effects that limit the MOS device performance in terms of capacitance and leakage current. Moreover, these ultra thin oxide MOS structures are prone to new degradation processes that could reduce their operation lifetime. In this paper, the major limitations raised by the scaling of the gate dielectrics in CMOS technologies are briefly reviewed in terms of MOS capacitance, reliability and new materials issues. More specifically, we first focus on the limitations raised by physical phenomena inherent to MOS capacitors such as polysilicon depletion and quantum effects (carrier confinement and tunneling), impacting their performances. We then address the limitations related to the reliability concerns such as wearout, breakdown, quasi-breakdown, stress-induced leakage current, determining the device lifetime. Finally, the new materials currently envisaged, as replacement solutions in order to overcoming the difficulties due to the gate oxide scaling will be discussed. In particular, the possible solutions based on alternate high permittivity gate dielectrics and metallic gate materials will be emphasized. 相似文献
3.
In this paper, we describe a facile method for preparation of ZnSe quantum dots (QDs) using an inexpensive and biocompatible source of acetyl cysteine in aqueous media. The structural properties of the ZnSe QDs have been characterized using XRD, FT-IR, and TEM techniques. The optical properties of the as-prepared QDs were found to be size-dependent, due to the strong confinement regime at relatively low refluxing time. Effect of solution pH and refluxing temperature on absorption and emission characteristics of the ZnSe QDs was studied. The empirical effective mass approximation also reveals that, both solution pH and refluxing temperature parameters would effect on ZnSe QDs growth, and increase their size. However, the influence of the solution pH was found to be more prominent. Water-solubility, high emission intensity and sub-10 nm nanocrystals size are the most essential features that suggest our synthesized aqueous-based ZnSe QDs (with a very cost-effective and biocompatible capping agent) can be utilized for biological intentions. 相似文献
4.
脉冲功率技术的重要发展方向是高功率密度、紧凑小型化和高稳定可靠。液体介质由于具有绝缘强度高、易流动、快恢复、散热性好等方面的特点,广泛应用于脉冲形成线型紧凑小型脉冲功率源的电容储能器件作为储能介质。主要围绕紧凑小型脉冲功率源ARC系列的技术难题,开展了关键技术、系统研发及其工程应用等方面的工作。首先,提出了基于液体介质和慢波结构的形成线,采用场均匀和绝缘配合技术,研制出紧凑小型脉冲功率源ARC-01和ARC-02,输出功率1~2 GW、脉冲宽度5~30 ns、重复频率1~100 Hz,紧凑化水平较国际先进同类装置最多提高了2倍。之后,以凑小型脉冲功率源为核心搭建液体介质击穿测试平台,针对变压器油、蓖麻油、甘油、碳酸丙烯酯等常见液体介质,开展了微秒脉冲击穿特性研究,采用统计分析方法建立了数据库,以“小成本”换取“高可靠性”;并采用超高速光学诊断方法,将击穿瞬间流注、冲击波、亚微观断裂面产生、传播、截止过程与张力理论结合,建立了液体介质击穿物理模型。最后,成功将紧凑小型脉冲功率源应用于驱动宽带/窄带微波产生、碳纤维阴极稳定性及寿命测试。 相似文献
5.
Sheng Jiang Andrew G. Krygier Douglass W. Schumacher Kramer U. Akli Richard R. Freeman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2014,68(10):1-8
A new type of a coaxial multi-layer plasmonic waveguide is proposed. The mode propagation properties are analyzed at the communication working wavelength. Theoretical investigations reveal that the enhanced optical confinement can be achieved in the two low-index dielectric media layers. The mode size can be sub- or deep sub-wavelength scale. The mode propagation loss can be well compensated by replacing the high-index dielectric media with gain material to achieve longer propagation length with better mode confinement. The comparisons of the mode properties between the proposed waveguide and waveguides studied in the published literatures are also considered. These investigations potentially lay the groundwork for the further applications of nanowire type multilayer hybrid structures. This structure could also enable various applications such asnanophotonic waveguides, high-quality nanolasers, and optical trapping and biosensors. 相似文献
6.
S. Reyné G. Duchateau J. Y. Natoli L. Lamaignère 《Applied physics. B, Lasers and optics》2012,109(4):695-706
This study addresses the initiation of laser-induced breakdown of dielectric materials in the nanosecond regime under multi-wavelength conditions. In particular, the competition between multi-photon absorption and electronic avalanche as ionization mechanisms in KDP crystal is studied. Since they are both dependent on the laser frequency and intensity of incident radiations, we carried out two experiments: in mono-wavelength configuration at 1,064?nm and in multi-wavelengths configuration applying the simultaneous mixing of 1,064 and 355?nm radiations with various fluence ratios. To interpret experimental data, a model based on heat transfer and which includes ionization processes has been developed for both configurations. The comparison between experiments and modeling results first indicates that avalanche can be responsible for optical breakdown at 1,064?nm. Then, the study underlines the existence of a coupling effect in the multi-wavelength configuration where multi-photon absorption and electronic avalanche both contribute to the breakdown. From a general point of view, the model accounts for the experimental trends and particularly reveals that the electronic recombination timescale may have an important role in the scenario of nanosecond laser-induced breakdown. 相似文献
7.
《Current Applied Physics》2019,19(7):787-793
Nanocrystalline PbTe thin films were deposited on a glass substrate by thermal evaporation technique with two thicknesses namely, 45 and 250 nm. The structural studies revealed that the films have nanocrystalline cubic structure and the particle size was found to be 11 and 20.7 nm, for low and high thicknesses respectively. The FE-SEM study shows that the surface grains increase for higher thickness film. This indicates that samples lying under the strong regime of confinement for PbTe thin films. The optical properties confirm the occurrence of confinement process as the optical band gap are 1.67 and 0.9 eV for 45 and 250 nm films, respectively. The dielectric results indicated that the conductivity increases by about two orders of magnitude with increasing the thickness from 45 to 250 nm. Moreover, the permittivity shows a higher dispersion step at lower frequencies in both samples due to the hopping conduction mechanism in addition to the interfacial polarization in such heterogeneous structures. Another small dispersion step is noticed in case of the lower thickness. It is attributed to the polarization of the accumulated charge carriers near the grain boundaries interfaces. No indication of any electrode phenomena in both samples is shown here. 相似文献
8.
We measure fluorescence lifetimes of emitters embedded in isolated single dielectric nanospheres. By varying the diameters of the spheres from 100 nm to 2 microm and by modifying their dielectric surrounding, we demonstrate a systematic change of paradigm in the spontaneous emission rate, as we cross the border from the superwavelength regime of Mie resonances to the nanoscopic realm of Rayleigh scattering. Our data show inhibition of the spontaneous emission up to 3 times and are in excellent agreement with the results of analytical calculations. 相似文献
9.
A. V. Bulanov I. G. Nagorny 《Bulletin of the Russian Academy of Sciences: Physics》2014,78(2):160-163
Results from experimental investigations of acoustic emission from the optical breakdown zone in liquid formed by laser radiation at a wavelength of 532 nm are presented. The linear dependence of the acoustic pressure on the laser pulse energy is revealed. It is shown that the effect of an additional source of sound at a frequency of 37 kHz enhances the acoustic emission from the optical breakdown zone. 相似文献
10.
综合考虑发射电子的发射能量、发射角度及微波场的相位分布等因素,运用统计方法,研究了介质表面单边次级电子倍增过程中次级电子数目、瞬时直流场、渡越时间、微波场的沉积功率等次级电子倍增特征物理量随碰撞次数的变化过程,仿真分析了不同夹角、不同反射系数对次级电子倍增的影响。研究结果表明:当倾斜直流场一定时,微波场的反射系数越小,雪崩击穿的延迟时间越长,饱和状态下的次级电子数目越大;微波场一定时,当直流电场平行于介质板表面时,直流电场幅值越大,雪崩击穿的延迟时间越长,饱和状态下的次级电子数目越大,但当电场强度超过一定值时,次级电子倍增现象不再发生,当直流场垂直介质板表面,直流电场幅值越大,雪崩击穿的延迟时间越长,饱和状态下的次级电子数目越小,幅值超过一定值时,次级电子倍增现象同样不会发生。 相似文献