| 1. |
- Bruhn, Benjamin, et al.
(författare)
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Blinking Statistics and Excitation-Dependent Luminescence Yield in Si and CdSe Nanocrystals
- 2014
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:4, s. 2202-2208
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Tidskriftsartikel (refereegranskat)abstract
- ON-OFF intermittency or blinking is a phenomenon observed in single quantum emitters, which reduces their overall light emission. Even though it seems to be a fundamental property of quantum dots (QDs), substantial differences can be found in the blinking statistics of different nanocrystals. This work compares the blinking of numerous single, oxide-capped Si nanocrystals with that of CdSe/ZnS core-shell nanocrystals, measured under the same conditions in the same experimental system and over a broad range of excitation power densities. We find that ON- and OFF-times can be described by exponential statistics in Si QDs, as opposed to power-law statistics for the CdSe nanocrystals. The type of blinking (power-law or monoexponential) does not depend on excitation but seems to be an intrinsic property of the material system. Upon increasing excitation power, the duty cycle of Si quantum dots remains constant, whereas it decreases for CdSe nanocrystals, which is readily explained by blinking statistics. Both ON-OFF and OFF-ON transitions can be regarded as light-induced in Si/SiO2 QDs, while the OFF-ON transition in CdSe/ZnS nanocrystals is not stimulated by photons. The differences in blinking behavior in these systems will be discussed.
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| 2. |
- 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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| 3. |
- Sangghaleh, Fatemeh, et al.
(författare)
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Optical absorption cross section and quantum efficiency of a single silicon quantum dot
- 2013
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Ingår i: Nanotechnology VI. - : SPIE - International Society for Optical Engineering. - 9780819495631 ; , s. 876607-
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Konferensbidrag (refereegranskat)abstract
- Direct measurements of the optical absorption cross section (sigma) and exciton lifetime are performed on a single silicon quantum dot fabricated by electron beam lithography (EBL), reactive ion etching (RIE) and oxidation. For this aim, single photon counting using, an avalanche photodiode detector (APD) is applied to record photoluminescence (PL) intensity traces under pulsed excitation. The PL decay is found to be of a mono-exponential character with a lifetime of 6.5 mu s. By recording the photoluminescence rise time at different photon fluxes the absorption cross could be extracted yielding a value of 1.46x10(-14)cm(2) under 405 nm excitation wavelength. The PL quantum efficiency is found to be about 9% for the specified single silicon quantum dot.
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| 4. |
- Sychugov, Ilya, et al.
(författare)
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Exciton localization in doped Si nanocrystals from single dot spectroscopy studies
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 86:7, s. 075311-
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Tidskriftsartikel (refereegranskat)abstract
- The results of low-temperature photoluminescence characterization of single silicon nanocrystals prepared from highly doped silicon-on-insulatorwafers are presented. The effect of B, P, As, and Sb impurities on ensemble as well as individual emission spectra are determined by comparison with the line shapes of undoped nanocrystals. From the statistical analysis of the luminescence spectra, the donor ionization energies for nanocrystals emitting in the range of 1.5-2.0 eV are estimated to be 140-200 meV, while the exciton-impurity binding energy for As- and Sb-doped nanocrystals is found to be about 40-45 meV.
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| 5. |
- Sychugov, Ilya
(författare)
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Luminescent silicon nanocrystals as downconverters for photovoltaic and lighting applications
- 2014
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Ingår i: Optics InfoBase Conference Papers. - : OSA - The Optical Society. - 9780960038008
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Konferensbidrag (refereegranskat)abstract
- Nanocrystals offer new functionalities for optoelectronics. Ensemble and single-dot measurements of chemically-synthesized silicon nanocrystals revealed high quantum yield, narrow homogeneous linewidth, and large Stokes shift, confirming application feasibility for these non-toxic and abundant material nanoparticles.
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| 6. |
- Sychugov, Ilya, et al.
(författare)
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Manifold Enhancement of Electron Beam Induced Deposition Rate at Grazing Incidence
- 2010
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Ingår i: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 21:2, s. 025303-
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Tidskriftsartikel (refereegranskat)abstract
- It is shown how a significant drawback of the electron beam induced deposition technique, namely its low deposition rate, can be circumvented. By tilting a sample, a larger part of the primary electron beam energy becomes dissipated closer to the interface. This in turn increases the emission of secondary electrons, largely responsible for the deposition of the adsorbed molecule components on the surface. An order of magnitude increase in the deposition rate is reported in the fabrication of metal nanowires from organic precursor gas.
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| 7. |
- Sychugov, Ilya, et al.
(författare)
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Photoluminescence measurements of zero-phonon optical transitions in silicon nanocrystals
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 84:12, s. 125326-
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Tidskriftsartikel (refereegranskat)abstract
- Optical transitions in silicon nanocrystals with different surface passivations were probed at low temperatures on a single-particle level. A type of quasidirect recombination process, different from the quantum-confined exciton transition, is identified. The luminescence spectra have different emission energies, but the contribution of a no-phonon transition is significantly higher than expected from the quantum-confinement model. Its relative strength was found to be temperature dependent, suggesting spatial localization of excitons as a possible origin.
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| 8. |
- Sychugov, Ilya, et al.
(författare)
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Sub-10 nm crystalline silicon nanostructures by electron beam induced deposition lithography
- 2010
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Ingår i: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 21:28, s. 285307-
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Tidskriftsartikel (refereegranskat)abstract
- A novel top-down approach for the controllable fabrication of semiconductor nanostructures exhibiting quantum effects is described. By decomposing metal-rich precursor gas molecules with an electron beam, a sub-10 nm metal pattern can be formed and subsequently transferred to a semiconductor substrate. In such a way monocrystalline silicon nanodots and nanowires are produced as revealed by transmission electron microscopy. It is also shown how through controlled thermal or chemical oxidation the nanostructure surface can be passivated. By providing direct access to the sub-10 nm size range this method possesses promising potential for application in the quantum dot and nanoelectronics fields.
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| 9. |
- Sychugov, Ilya, et al.
(författare)
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Ultranarrow Luminescence Linewidth of Silicon Nanocrystals and Influence of Matrix
- 2014
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 1:10, s. 998-1005
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Tidskriftsartikel (refereegranskat)abstract
- The luminescence linewidth of individual silicon nanocrystals was characterized by single-dot spectroscopy, and an ultranarrow linewidth of similar to 200 mu eV at 10 K was found. This value is, in fact, limited by system resolution and represents only the upper limit of the homogeneous linewidth. In addition, the effect of the matrix was investigated for nanocrystals coated with organic ligands, embedded in silicon dioxide, as well as for nanocrystals with only a thin passivating layer. It was found that, depending on the matrix, the room-temperature bandwidth may vary by an order of magnitude, where values as small as similar to 12 meV (similar to 5 nm) at 300 K were detected for nanocrystals with a thin passivation. The observed values for silicon nanocrystals are similar and even surpass some of those for direct-band-gap quantum dots. The narrow linewidth at room temperature enables the use of silicon nanocrystals for nontoxic narrow-band labeling of biomolecules and for application as phosphors in white-light-emitting devices.
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| 10. |
- Zhang, Miao, et al.
(författare)
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Oxidation of nanopores in a silicon membrane : self-limiting formation of sub-10nm circular openings
- 2014
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Ingår i: Nanotechnology. - : Institute of Physics (IOP). - 0957-4484 .- 1361-6528. ; 25:35, s. 355302-
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Tidskriftsartikel (refereegranskat)abstract
- We describe a simple but reliable approach to shrink silicon nanopores with nanometer precision for potential high throughput biomolecular sensing and parallel DNA sequencing. Here, nanopore arrays on silicon membranes were fabricated by a self-limiting shrinkage of inverted pyramidal pores using dry thermal oxidation at 850 degrees C. The shrinkage rate of the pores with various initial sizes saturated after 4 h of oxidation. In the saturation regime, the shrinkage rate is within +/- 2 nm h(-1). Oxidized pores with an average diameter of 32 nm were obtained with perfect circular shape. By careful design of the initial pore size, nanopores with diameters as small as 8 nm have been observed. Statistics of the pore width show that the shrinkage process did not broaden the pore size distribution; in most cases the distribution even decreased slightly. The progression of the oxidation and the deformation of the oxide around the pores were characterized by focused ion beam and electron microscopy. Cross-sectional imaging of the pores suggests that the initial inverted pyramidal geometry is most likely the determining factor for the self-limiting shrinkage.
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