| 1. |
- Bruhn, Benjamin, et al.
(författare)
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Blinking Statistics of Silicon Quantum Dots
- 2011
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 11:12, s. 5574-5580
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Tidskriftsartikel (refereegranskat)abstract
- The blinking statistics of numerous single silicon quantum dots fabricated by electron-beam lithography, plasma etching, and oxidation have been analyzed. Purely exponential on- and off-time distributions were found consistent with the absence of statistical aging. This is in contrast to blinking reports in the literature where power-law distributions prevail as well as observations of statistical aging in nanocrystal ensembles. A linear increase of the switching frequency with excitation power density indicates a domination of single-photon absorption processes, possibly through a direct transfer of charges to trap states without the need for a bimolecular Auger mechanism. Photoluminescence saturation with increasing excitation is not observed; however, there is a threshold in excitation (coinciding with a mean occupation of one exciton per nanocrystal) where a change from linear to square-root increase occurs. Finally, the statistics of blinking of single quantum dots in terms of average on-time, blinking frequency and blinking amplitude reveal large variations (several orders) without any significant correlation demonstrating the individual microscopic character of each quantum dot.
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| 2. |
- Bruhn, Benjamin, et al.
(författare)
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Controlled fabrication of individual silicon quantum rods yielding high intensity, polarized light emission
- 2009
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Ingår i: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 20:50, s. 1-5
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Tidskriftsartikel (refereegranskat)abstract
- Elongated silicon quantum dots (also referred to as rods) were fabricated using a lithographic process which reliably yields sufficient numbers of emitters. These quantum rods are perfectly aligned and the vast majority are spatially separated well enough to enable single-dot spectroscopy. Not only do they exhibit extraordinarily high linear polarization with respect to both absorption and emission, but the silicon rods also appear to luminesce much more brightly than their spherical counterparts. Significantly increased quantum efficiency and almost unity degree of linear polarization render these quantum rods perfect candidates for numerous applications.
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| 3. |
- Bruhn, Benjamin, et al.
(författare)
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Transition from silicon nanowires to isolated quantum dots : Optical and structural evolution
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 87:4, s. 045404-
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of the structural and optical properties of a silicon core in oxidized nanowalls is investigated as a function of oxidation time. The same individual nanostructures are characterized after every oxidation step in a scanning electron microscope and by low-temperature photoluminescence, while a representative sample is also imaged in a transmission electron microscope. Analysis of a large number of recorded single-dot spectra and micrographs allows to identify delocalized and localized exciton emission from a nanowire as well as confined exciton emission of a nanocrystal. It is shown how structural transitions from one-to zero-dimensional confinement affect single-nanostructure optical fingerprints.
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| 4. |
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| 5. |
- Janda, Petr, et al.
(författare)
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Modified spontaneous emission of silicon nanocrystals embedded in artificial opals
- 2007
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 40:19, s. 5847-5853
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Tidskriftsartikel (refereegranskat)abstract
- Si nanocrystals (NCs) were embedded in synthetic silica opals by means of Si-ion implantation or opal impregnation with porous-Si suspensions. In both types of sample photoluminescence (PL) is strongly Bragg-reflection attenuated (up to 75%) at the frequency of the opal stop-band in a direction perpendicular to the ( 1 1 1) face of the perfect hcp opal structure. Time-resolved PL shows a rich distribution of decay rates, which contains both shorter and longer decay components compared with the ordinary stretched exponential decay of Si NCs. This effect reflects changes in the spontaneous emission rate of Si NCs due to variations in the local density of states of real opal containing defects.
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| 6. |
- Sychugov, Ilya, et al.
(författare)
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Light emission from silicon nanocrystals: probing a single quantum do
- 2006
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 252:15, s. 5249-5253
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of low-temperature photoluminescence measurements performed on single silicon nanocrystals is presented. The luminescence emission linewidth of Si nanocrystals is found to be less than thermal broadening at low temperature, confirming the atomic-like nature of their energetic states. Beside the main peak the low-temperature spectra reveal a similar to 6 meV replica, the origin of which is discussed. For some of the investigated dots, we also observe a similar to 60 meV transverse optical (TO) phonon replica. The regular arrangement of individual nanocrystals used in this work enables combined high-resolution transmission electron microscopy (TEM) and low-temperature photoluminescence characterization of the same single quantum dot.
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| 7. |
- Sychugov, Ilya, et al.
(författare)
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Luminescence blinking of a Si quantum dot in a SiO2 shell
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : The American Physical Society. - 1098-0121 .- 1550-235X. ; 71:11, s. 115331-1-115331-5
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Tidskriftsartikel (refereegranskat)abstract
- The phenomenon of on-off luminescence intermittency - blinking - in silicon nanocrystals was studied using a single-dot microphotoluminescence technique. From recordings of the luminescence intensity trace, on- and off-time distributions were extracted revealing exponential behavior, as expected for systems with blinking of a purely random nature. The corresponding switching rates for on-off and off-on processes exhibit different dependence on the excitation intensity. While the on-off switching rate grows quadratically with the excitation, the inverse process is nearly pumping power independent. Experimental findings are interpreted in terms of a dot "charging" model, where a carrier may become trapped in the surrounding matrix due to thermal and Auger-assisted processes. Observed blinking kinetics appear to be different from that of porous silicon particles.
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| 8. |
- Sychugov, Ilya, et al.
(författare)
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Narrow luminescence linewidth of a silicon quantum dot
- 2005
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 94:8, s. 087405 (1)-087405 (4)
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Tidskriftsartikel (refereegranskat)abstract
- Single-dot luminescence spectroscopy was used to study the emission linewidth of individual silicon nanocrystals from low temperatures up to room temperature. The results show a continuous line narrowing towards lower temperatures with a linewidth as sharp as 2 meV at 35 K. This value, clearly below the thermal broadening at this temperature, proves the atomiclike emission from silicon quantum dots subject to quantum confinement. The low temperature measurements further reveal a similar to6 meV replica, whose origin is discussed. In addition, an similar to60 meV TO-phonon replica was detected, which is only present in a fraction of the dots.
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| 9. |
- Sychugov, Ilya, et al.
(författare)
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Single dot optical spectroscopy of silicon nanocrystals: Low temperature measurements
- 2005
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Ingår i: Optical materials (Amsterdam). - : Elsevier BV. - 0925-3467 .- 1873-1252. ; 27:5, s. 973-976
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Tidskriftsartikel (refereegranskat)abstract
- Single dot spectroscopy allows studying properties of a single nanocrystal avoiding inhomogeneous broadening of the emission band. Here, data obtained by this technique for Si nanocrystals fabricated by electron beam lithography, plasma etching and subsequent size-reduction by oxidation are presented. First, blinking (on–off intermittence) of the luminescence was observed for most individual nanocrystals, although some exhibited relatively stable luminescence. As a result of the quantum confinement effect spectra with different emission wavelengths for different nanocrystals were recorded. While at room temperature the full width at half-maximum of the nanocrystal emission peaks was measured to be 100–150 meV, at 80 K the linewidth for some dots appeared to be about 25 meV only. The observed temperature dependence of the homogeneous linewidth may lead to an understanding of the exciton–phonon interaction in indirect band-gap quantum dots.
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| 10. |
- Valenta, Jan, et al.
(författare)
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Coexistence of 1D and Quasi-0D Photoluminescence from Single Silicon Nanowires
- 2011
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 11:7, s. 3003-3009
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Tidskriftsartikel (refereegranskat)abstract
- Single silicon nanowires (Si-NWs) prepared by electron-beam lithography and reactive-ion etching are investigated by imaging optical spectroscopy under variable temperatures and laser pumping intensities. Spectral images of individual Si-NWs reveal a large variability of photoluminescence (PL) along a single Si-NW. The weaker broad emission band asymmetrically extended to the high-energy side is interpreted to be due to recombination of quasi-free 1D excitons while the brighter localized emission features (with significantly variable peak position, width, and shape) are due to localization of electron hole pairs in surface protrusions acting like quasi-0D centers or quantum dots (QDs). Correlated PL and scanning electron microscopy images indicate that the efficiently emitting QDs are located at the Si-NW interface with completely oxidized neck of the initial Si wall. Theoretical fitting of the delocalized PL emission band explains its broad asymmetrical band to be due to the Gaussian size distribution of the Si-NW diameter and reveals also the presence of recombination from the Si-NW excited state which can facilitate a fast capture of excitons into QD centers.
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