Optical absorption cross sections of Si nanocrystals

Kovalev, D.; Diener, J.; Heckler, H.; Polisski, G.; Künzner, N.; Koch, F.

doi:10.1103/physrevb.61.4485

Cited by 181 publications

(174 citation statements)

References 11 publications

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“…At the range of excitation wavelengths in Figure 1, the extinction cross section of np-Au is much higher than the silicon nanocrystal (nc-Si) absorbance cross section measured at an emission wavelength of 780 nm by Garcia et al 3 (solid triangles), Kovalev et al 4 (solid squares), and the present work (open circle). The trend in nc-Si absorbance cross section is fit to a decreasing exponential (dotted line), and it is found that the decreasing nc-Si cross sections obey a similar trend to the np-Au cross sections, but that np-Au has a larger absorbance cross section than nc-Si at all wavelengths investigated.…”

contrasting

confidence: 49%

Enhanced Radiative Emission Rate and Quantum Efficiency in Coupled Silicon Nanocrystal-Nanostructured Gold Emitters

et al. 2005

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i Biteen, et al., Enhanced radiative emission rate and quantum efficiency… SUPPORTING INFORMATION:The nanoporous gold (np-Au) film was characterized optically with a Sentech SE-850 spectroscopic ellipsometer. Transmission and reflection spectra were used to calculate the absorbance spectrum, and spectroscopic ellipsometry confirmed that the film's thickness was 150 nm. These measurements were used to derive the extinction cross section spectrum in Figure 1 (red line), assuming, based on SEM data, that the average np-Au particle in the 50% Au/50% air film is a sphere of radius 10 nm. A 150-nm thick film of continuous Au deposited on SiO 2 by evaporation was also studied with the Sentech SE-850, and its transmission and reflection spectra were used to determine its absorbance spectrum. The np-Au film has a broad extinction spectrum that shows a peak between 300 and 400 nm, and a tail that decreases with increasing wavelength through most of the visible. Though the absorbance cross sections of both np-and bulk Au peak at similar wavelengths, the percent absorbance of np-Au is more than 2.5 times that of planar bulk Au throughout the visible, and np-Au absorbs over a broader wavelength range than bulk Au. Indeed, we found for nc-Si in SiO 2 coupled to a planar, continuous film of bulk Au that the luminescence intensity was decreased at all separation distances, relative to a reference sample. 1 According to Mie-Gans theory 2 , the measured np-Au extinction cross section in Figure 1 is consistent with the aggregate surface plasmon resonant response for a continuum of features including Au spheres and spheroids in air and spherical and spheroidal voids in gold.

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confidence: 49%

Enhanced Radiative Emission Rate and Quantum Efficiency in Coupled Silicon Nanocrystal-Nanostructured Gold Emitters

et al. 2005

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“…Moreover, the A value obtained from fitting to Fig. 5 is unfeasibly large: for a cluster cross section in the region of 10 −15 -10 −16 cm 2 , as is commonly used in the literature, 22 we would obtain a lifetime of the order of 0.1-1 ms. Measurements of the nanocluster PL lifetime in our sample showed it instead to be of the order of our system resolution ͑5-10 s͒, which would imply a cross section around 10 −13 cm 2 -such a cross section is simply too high to be plausible. As an aside, it should be noted that there is considerable variation in the luminescence lifetimes of silicon nanoclusters reported in the literature.…”

Section: Analysis and Refinement Of The Basic Modelmentioning

confidence: 99%

Generalized rate-equation analysis of excitation exchange between silicon nanoclusters and erbium ions

et al. 2008

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We discuss the use of rate equations to analyze the sensitization of erbium luminescence by silicon nanoclusters. In applying the general form of second-order coupled rate-equations to the Si nanocluster-erbium system, we find that the photoluminescence dynamics cannot be described using a simple rate equation model. Both rise and fall times exhibit a stretched exponential behavior, which we propose arises from a combination of a strongly distance-dependent nanocluster-erbium interaction, along with the finite size distribution and indirect band gap of the silicon nanoclusters. Furthermore, the low fraction of erbium ions that can be excited nonresonantly is a result of the small number of ions coupled to nanoclusters.

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“…The reason is probably because large nanocrystals have smaller cross section ͑per Si unit cell͒ for absorption and the theory also predicts a smaller transition rate ͑oscillator strength͒ for such large sizes, although no experimental proof still exists for this interpretation. 45,46 …”

Section: A Photoluminescence Versus Supersaturation and Link With Stmentioning

confidence: 99%

Influence of average size and interface passivation on the spectral emission of Si nanocrystals embedded in SiO2

Fernández

López

Garcı́a

et al. 2002

Journal of Applied Physics

260

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The correlation between the structural ͑average size and density͒ and optoelectronic properties ͓band gap and photoluminescence ͑PL͔͒ of Si nanocrystals embedded in SiO 2 is among the essential factors in understanding their emission mechanism. This correlation has been difficult to establish in the past due to the lack of reliable methods for measuring the size distribution of nanocrystals from electron microscopy, mainly because of the insufficient contrast between Si and SiO 2 . With this aim, we have recently developed a successful method for imaging Si nanocrystals in SiO 2 matrices. This is done by using high-resolution electron microscopy in conjunction with conventional electron microscopy in dark field conditions. Then, by varying the time of annealing in a large time scale we have been able to track the nucleation, pure growth, and ripening stages of the nanocrystal population. The nucleation and pure growth stages are almost completed after a few minutes of annealing time at 1100°C in N 2 and afterward the ensemble undergoes an asymptotic ripening process. In contrast, the PL intensity steadily increases and reaches saturation after 3-4 h of annealing at 1100°C. Forming gas postannealing considerably enhances the PL intensity but only for samples annealed previously in less time than that needed for PL saturation. The effects of forming gas are reversible and do not modify the spectral shape of the PL emission. The PL intensity shows at all times an inverse correlation with the amount of P b paramagnetic centers at the Si-SiO 2 nanocrystal-matrix interfaces, which have been measured by electron spin resonance. Consequently, the P b centers or other centers associated with them are interfacial nonradiative channels for recombination and the emission yield largely depends on the interface passivation. We have correlated as well the average size of the nanocrystals with their optical band gap and PL emission energy. The band gap and emission energy shift to the blue as the nanocrystal size shrinks, in agreement with models based on quantum confinement. As a main result, we have found that the Stokes shift is independent of the average size of nanocrystals and has a constant value of 0.26Ϯ0.03 eV, which is almost twice the energy of the Si-O vibration. This finding suggests that among the possible channels for radiative recombination, the dominant one for Si nanocrystals embedded in SiO 2 is a fundamental transition spatially located at the Si-SiO 2 interface with the assistance of a local Si-O vibration.

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Optical absorption cross sections of Si nanocrystals

Cited by 181 publications

References 11 publications

Enhanced Radiative Emission Rate and Quantum Efficiency in Coupled Silicon Nanocrystal-Nanostructured Gold Emitters

Enhanced Radiative Emission Rate and Quantum Efficiency in Coupled Silicon Nanocrystal-Nanostructured Gold Emitters

Generalized rate-equation analysis of excitation exchange between silicon nanoclusters and erbium ions

Influence of average size and interface passivation on the spectral emission of Si nanocrystals embedded in SiO2

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