Silicon quantum dots (SiQDs) are semiconductor Si nanoparticles ranging from 1 to 10 nm that hold great applicative potential as optoelectronic devices and fluorescent bio-marking agents due to their ability to fluoresce blue and red light. Their biocompatibility compared to conventional toxic Group II-VI and III-V metal-based quantum dots makes their practical utilization even more attractive to prevent environmental pollution and harm to living organisms. This work focuses on their possible use for light-emitting diode (LED) manufacturing. Summarizing the main achievements over the past few years concerning different Si quantum dot synthetic methods, LED formation and characteristics, and strategies for their stabilization by microencapsulation and modification of their surface by specific ligands, this work aims to provide guidance en route to the development of the first stable Si-based light-emitting diodes.

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We formulate a general multi-mode Gaussian operator basis for fermions, to enable a positive phase-space representation of correlated Fermi states. The Gaussian basis extends existing bosonic phase-space methods to Fermi systems and thus allows first-principles dynamical or equilibrium calculations in quantum many-body Fermi systems. We prove the completeness of the basis and derive differential forms for products with one-and two-body operators. Because the basis satisfies fermionic superselection rules, the resulting phase space involves only c-numbers, without requiring anticommuting Grassmann variables. Furthermore, because of the overcompleteness of the basis, the phase-space distribution can always be chosen positive. This has important consequences for the sign problem in fermion physics.

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The damage threshold and damage mechanism of extreme-ultraviolet Sc͞Si multilayer mirror coatings are investigated with focused nanosecond pulses at 46.9-nm radiation from a compact capillary-discharge laser. Damage threshold f luences of ϳ0.08 J͞cm 2 are measured for coatings deposited on both borosilicate glass and Si substrates. The use of scanning and transmission electron microscopy and small-angle x-ray diffraction techniques reveals the thermal nature of the damage mechanism. The results are relevant to the use of newly developed high-f lux extreme-ultraviolet sources in applications. However, the damage to these mirrors when exposed to high peak powers of EUV light has not been studied to our knowledge. This problem is now of particular relevance because the peak power and f luence of EUV sources have recently increased significantly (for example, the radiation f luence at the exit of a capillary-discharge Ne-like Ar laser operating at 46.9 nm can exceed 1 J͞cm 2 ) and is soon expected to achieve unprecedented values with the commissioning of EUV free-electron lasers. 2 -4 In this Letter we report results of the study of the optical damage mechanisms and the damage threshold for Sc͞Si EUV mirrors exposed to high-power EUV laser radiation. The study was conducted by focusing the output of a tabletop capillary-discharge Ne-like Ar laser emitting nanosecond duration pulses at a wavelength of 46.9 nm. The resulting damage to the multilayer coatings exposed to the EUV beam was analyzed with scanning electron microscopy (SEM), transmission electron microscopy (TEM), and small-angle x-ray diffraction (l 0.154 nm) techniques. Our results show that multilayer coatings on Si and borosilicate glass have similar damage threshold values of ϳ0.08 J͞cm 2 , compared with the 0.7 J͞cm 2 found necessary to damage a bare Si substrate. These values are similar to the thresholds found in Mo͞Si, W͞C, and W͞Si coatings measured at much shorter wavelengths. 6,7The Sc͞Si multilayers were deposited by dc magnetron sputtering at 3 mTorr of Ar pressure on superpolished borosilicate glass (surface roughness of s ϳ 0.4 nm) and on Si wafers (s ϳ 0.6 nm). The multilayers on borosilicate glass consisted of ten periods of Sc͞Si layers, each with a thickness of ϳ26.7 nm and a ratio of layer thickness of H͑Sc͒͞H͑Si͒ ϳ 0.7. A top 5-nm-thick Si protection layer capped the multilayers. The multilayer coatings deposited on Si consisted of 33 periods of Sc͞Si pairs with the same parameters as those deposited on borosilicate glass. In these structures the crystalline Sc layers were always separated from the amorphous Si layers by ϳ3 nm of amorphous ScSi interface layers formed by interdiffusion. The experimental setup used to irradiate the samples was described in Ref. 9. The laser emission was focused onto the target surface with a spherical R 10 cm Sc͞Si multilayer-coated mirror that was 2.5 cm in diameter and positioned at normal incidence. The ref lectivity of this particular mirror was measured to be ϳ30% at 46.9 nm. The capillarydischar...