| 1. |
- Doyle, J P, et al.
(författare)
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Observation of near-surface electrically active defects in n-type 6H-SiC
- 1998
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 83, s. 3649-3651
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Tidskriftsartikel (refereegranskat)abstract
- In n-type 6H-SiC epitaxial layers grown by vapor phase epitaxy, we find that in contrast to the majority of the epitaxial layer, where electrically active defects are observed with a concentration less than 1 X 10(-13) cm(-3), a region near the front surface contains defects with concentrations approaching 10(14) cm(-3). A relationship between the near-surface defects and metallic impurities is suggested by a Ti concentration of 1 X 10(16) cm(-3) in this region. The high concentration of near surface defects is found to significantly reduce the carrier lifetime. (C) 1998 American Institute of Physics. [S0021-8979(98)03007-2].
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| 2. |
- Valenta, J., et al.
(författare)
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Photonic band-gap effects on photoluminescence of silicon nanocrystals embedded in artificial opals
- 2003
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 93:8, s. 4471-4474
-
Tidskriftsartikel (refereegranskat)abstract
- Si nanocrystals were formed in synthetic opals by Si-ion implantation and their optical properties studied using microphotoluminescence and reflection techniques. The properties of areas with high crystalline quality are compared with those of disordered regions of samples. The photoluminescence spectrum from Si nanocrystals embedded in silica spheres is narrowed by the inhibition of emission at wavelengths corresponding to the opal photonic pseudoband gap (similar to690 nm). Measurements of photoluminescence spectra from individual implanted silica spheres is also demonstrated and the number of emitting Si nanocrystals in single brightly emitting spheres is estimated to be of the order of one thousand.
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| 3. |
- Alme, Tomas Nordheim, et al.
(författare)
-
Chronic fatigue syndromes: real illnesses that people can recover from
- 2023
-
Ingår i: Scandinavian Journal of Primary Health Care. - : TAYLOR & FRANCIS LTD. - 0281-3432 .- 1502-7724. ; 41:4, s. 372-376
-
Tidskriftsartikel (refereegranskat)abstract
- The Oslo Chronic Fatigue Consortium consists of researchers and clinicians who question the current narrative that chronic fatigue syndromes, including post-covid conditions, are incurable diseases. Instead, we propose an alternative view, based on research, which offers more hope to patients. Whilst we regard the symptoms of these conditions as real, we propose that they are more likely to reflect the brains response to a range of biological, psychological, and social factors, rather than a specific disease process. Possible causes include persistent activation of the neurobiological stress response, accompanied by associated changes in immunological, hormonal, cognitive and behavioural domains. We further propose that the symptoms are more likely to persist if they are perceived as threatening, and all activities that are perceived to worsen them are avoided. We also question the idea that the best way to cope with the illness is by prolonged rest, social isolation, and sensory deprivation.Instead, we propose that recovery is often possible if patients are helped to adopt a less threatening understanding of their symptoms and are supported in a gradual return to normal activities. Finally, we call for a much more open and constructive dialogue about these conditions. This dialogue should include a wider range of views, including those of patients who have recovered from them.
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| 4. |
- Badel, Xavier, et al.
(författare)
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Formation of pn junctions in deep silicon pores for X-ray imaging detector applications
- 2003
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 509:1-3, s. 96-101
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Tidskriftsartikel (refereegranskat)abstract
- The formation of pn junctions in deep silicon pores has been studied for a new concept of X-ray imaging detectors. The sensitive part of the device is an array of CsI(Tl) columns formed by filling a silicon matrix of pores having pn junctions in their walls. Under X-ray illumination, the CsI(TI) scintillator emits photons that are collected by the pn junctions. Relatively high signal collection efficiency is expected. However, the formation of pn junctions inside pore walls represents a challenging step in the detector fabrication. In this work pore matrices were fabricated in n-type silicon by deep reactive ion etching and by photo-electrochemical etching. The pn junctions were formed either by boron diffusion or deposition of boron doped poly-silicon. Various techniques were used to analyze the transverse depth profiles of boron atoms at different pore depths. The study shows successful results for pn-junctions formed both by diffusion and by poly-silicon deposition.
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| 5. |
- Badel, Xavier, et al.
(författare)
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Performance of scintillating waveguides for CCD-based X-ray detectors
- 2006
-
Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499 .- 1558-1578. ; 53:1, s. 3-8
-
Tidskriftsartikel (refereegranskat)abstract
- Scintillating films are usually used to improve the sensitivity of CCD-based X-ray imaging detectors. For an optimal spatial resolution and detection efficiency, a tradeoff has to be made on the film thickness. However, these scintillating layers can also be structured to provide a pixellated screen. In this paper, the study of CsI(TI)-filled pore arrays is reported. The pores are first etched in silicon, then oxidized and finally filled with CsI(TI) to form scintillating waveguides. The dependence of the detector sensitivity on pore depth, varied from 40 to 400 mu m here, follows rather well theoretical predictions. Most of the detectors produced in this work have a detective quantum efficiency of the incoming X-ray photons of about 25%. However, one detector shows that higher efficiency can be achieved approaching almost the theoretical limit set by Poisson statistics of the incoming X-rays. Thus, we conclude that it is possible to fabricate scintillating waveguides with almost ideal performance. Imaging capabilities of the detectors are demonstrated.
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| 6. |
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| 7. |
- Dev, Apurba, et al.
(författare)
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Electrokinetic effect for molecular recognition : A label-free approach for real-time biosensing
- 2016
-
Ingår i: Biosensors & bioelectronics. - : Elsevier. - 0956-5663 .- 1873-4235. ; 82, s. 55-63
-
Tidskriftsartikel (refereegranskat)abstract
- We present a simple and inexpensive method for label-free detection of biomolecules. The method monitors the changes in streaming current in a fused silica capillary as target biomolecules bind to immobilized receptors on the inner surface of the capillary. To validate the concept, we show detection and time response of different protein-ligand and protein-protein systems: biotin-avidin and biotin-streptavidin, barstar-dibarnase and Z domain-immunoglobulin G (IgG). We show that specific binding of these biomolecules can be reliably monitored using a very simple setup. Using sequential injections of various proteins at a diverse concentration range and as well as diluted human serum we further investigate the capacity of the proposed technique to perform specific target detection from a complex sample. We also investigate the time for the signal to reach equilibrium and its dependence on analyte concentration and demonstrate that the current setup can be used to detect biomolecules at a concentration as low as 100 pM without requiring any advanced device fabrication procedures. Finally, an analytical model based on diffusion theory has been presented to explain the dependence of the saturation time on the analyte concentration and capillary dimensions and how reducing length and inner diameter of the capillary is predicted to give faster detection and in practice also lower limit of detection.
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| 8. |
- Duan, M., et al.
(författare)
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Deposition of Scintillating Layers of Bismuth Germanate (BGO) Films for X-ray detector applications
- 1998
-
Ingår i: IEEE Transactions on Nuclear Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9499 .- 1558-1578. ; 45:3, s. 525-527
-
Tidskriftsartikel (refereegranskat)abstract
- Bi4Ge3O12 films were deposited by pulsed laser ablation on glass and SiO2/Si substrates. The crystal structures of the films depend on the deposition temperature. XRD patterns indicate that the films deposited at substrate temperature less than 400°C are amorphous. The as deposited amorphous films can be crystallized by post rapid thermal annealing (RTA) in the temperature window from 750°C to 800°C for 2 minutes in a oxygen ambient environment. RBS measurements confirm that the films have the same chemical composition as that of the target. The surface morphology of the films were characterized by atomic force microscopy (AFM)
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| 9. |
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| 10. |
- Galeckas, A, et al.
(författare)
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Evaluation of Auger recombination rate in 4H-SiC
- 1998
-
Ingår i: Proceedings of the 1997 7th International Conference on Silicon Carbide, III-Nitrides and Related Materials, ICSCIII.. ; , s. 533-536
-
Konferensbidrag (refereegranskat)
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| 11. |
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| 12. |
- Grivickas, P., et al.
(författare)
-
Carrier lifetime investigation in 4H-SiC grown by CVD and sublimation epitaxy
- 2001
-
Ingår i: Materials Science in Semiconductor Processing. - 1369-8001 .- 1873-4081. ; 4:03-jan, s. 191-194, s. 191-194
-
Tidskriftsartikel (refereegranskat)abstract
- Depth-resolved carrier lifetime measurements were performed in low-doped epitaxial layers of 4H silicon carbide samples. The technique used was a pump-and-probe technique where carriers are excited by an above-bandgap laser pulse and probed by free carrier absorption. Results from chemical vapour deposition samples show that lifetimes as high as 2 mus may be observed in the mid-region of 40 mum thick epilayers. For epilayers grown by the sublimation method decay transients were characterised by a fast (few nanoseconds) initial recombination, tentatively assigned to the 'true' lifetime, whereas a slow tail of several hundred microsecond decay time was assigned to trapping centres. From the saturation of this level at increased pumping we could derive the trapping concentration and their depth distribution peaking at the epilayer/substrate interface.
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| 13. |
- Grivickas, P, et al.
(författare)
-
Free Carrier Diffusion in 4H-SiC
- 2001
-
Ingår i: Materials Science Forum. - 0255-5476. ; 353/356, s. 353-356
-
Tidskriftsartikel (refereegranskat)
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| 14. |
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| 15. |
- Grivickas, V., et al.
(författare)
-
Spatially and time-resolved infrared absorption for optical and electrical characterization of indirect band gap semiconductors
- 2000
-
Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 364:02-jan, s. 181-185
-
Tidskriftsartikel (refereegranskat)abstract
- The current status of the spatially and time-resolved free-carrier absorption (FCA) method is provided. The FCA technique allows monitoring carrier dynamics in a time scale from nanoseconds to miliseconds by employing either collinear or orthogonal geometry between pump and probe beams. A high spatial resolution is achieved allowing in-depth carrier profiles to be extracted. The method is particularly suited for investigation of injection-dependent optical and recombination phenomena: band gap optical absorption, Shockley-Read-Hall (SRH) lifetime, Auger recombination coefficient, and the injection-dependent surface (interface) recombination velocity. We summarize important aspects of the technique demonstrating numerous measurements that have been implemented in studies of bulk Si, epilaxial 4H-SiC and porous silicon.
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| 16. |
- Hansson, Petra M., et al.
(författare)
-
Effect of surface depressions on wetting and interactions between hydrophobic pore array surfaces
- 2012
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:30, s. 11121-11130
-
Tidskriftsartikel (refereegranskat)abstract
- The surface structure is known to significantly affect the long-range capillary forces between hydrophobic surfaces in aqueous solutions. It is, however, not clear how small depressions in the surface will affect the interaction. To clarify this, we have used the AFM colloidal probe technique to measure interactions between hydrophobic microstructured pore array surfaces and a hydrophobic colloidal probe. The pore array surfaces were designed to display two different pore spacings, 1.4 and 4.0 ÎŒm, each with four different pore depths ranging from 0.2 to 12.0 ÎŒm. Water contact angles measured on the pore array surfaces are lower than expected from the Cassie-Baxter and Wenzel models and not affected by the pore depth. This suggests that the position of the three-phase contact line, and not the interactions underneath the droplet, determines the contact angle. Confocal Raman microscopy was used to investigate whether water penetrates into the pores. This is of importance for capillary forces where both the movement of the three-phase contact line and the situation at the solid/liquid interface influence the stability of bridging cavities. By analyzing the shape of the force curves, we distinguish whether the cavity between the probe and the surfaces was formed on a flat part of the surface or in close proximity to a pore. The pore depth and pore spacing were both found to statistically influence the distance at which cavities form as surfaces approach each other and the distance at which cavities rupture during retraction.
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| 17. |
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| 18. |
- Li, F., et al.
(författare)
-
Colloidal crystal wires from directed assembly
- 2005
-
Ingår i: Micro- and Nanosystems-Materials and Devices. - : Materials Research Society. - 1558998268 ; , s. 477-482
-
Konferensbidrag (refereegranskat)abstract
- Colloidal crystal wires with tubular-like packings are prepared by the directed assembly of spheres into cylindrical one-dimensional channels. Silica spheres are infiltrated into porous silicon membranes, treated with silane, and annealed. Single annealing cycles are found to result in colloidal crystal wires with varied packing geometries, while repeated annealing produces a thin translucent silica sheath around the wires. Packing in the wires varies with the relative channel diameter of the silicon membrane where typical wires contain 4 to 7 helical strands. Both chiral and achiral packing geometries are observed. The fabrication of these wires is discussed and the relationship between channel size and packing structure detailed.
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| 19. |
- Li, F., et al.
(författare)
-
Fabrication and assembly behavior of square microcapsules
- 2006
-
Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 18:3, s. 270-
-
Tidskriftsartikel (refereegranskat)abstract
- Square microcapsules have been fabricated within porous silicon membranes. The capsules float in water when released from the membrane (see Figure). Dry capsules float with one of their edges pointing down, but after uptake of water, they float face down; the edge-down capsules assemble end-to-end while the face-down capsules assemble face-to-face.
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| 20. |
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| 21. |
- Li, Yuanyuan, et al.
(författare)
-
Luminescent Transparent Wood
- 2017
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Ingår i: Advanced Optical Materials. - : John Wiley & Sons. - 2195-1071. ; 5:1
-
Tidskriftsartikel (refereegranskat)abstract
- Luminescent transparent wood is prepared by combining the complementary properties of naturally grown anisotropic porous wood and luminescent quantum dots. The wood structure introduces strong diffused luminescence and waveguiding, which can potentially be exploited for optoelectronic and photovoltaic applications, such as for planar illumination sources and luminescent buildings/furniture. Images below show the transparency, haze, and luminescence of quantum dot wood.
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| 22. |
- Marinins, Aleksandrs, et al.
(författare)
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All-optical intensity modulation in polymer waveguides doped with si quantum dots
- 2018
-
Ingår i: Optics InfoBase Conference Papers. - : Optical Society of America. - 9781557528209
-
Konferensbidrag (refereegranskat)abstract
- We demonstrate all-optical intensity modulation in integrated PMMA optical waveguides doped with silicon quantum dots. The 1550 nm probe signal is absorbed by free carriers excited in silicon quantum dots with 405 nm pump light.
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| 23. |
- Marinins, Aleksandrs, 1988-, et al.
(författare)
-
Free carrier absorption modulation in polymer waveguides doped with Si nanocrystals
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This work demonstrates all-optical intensity modulation in integrated optical polymer waveguides doped with Si nanocrystals. The modulation here is based on free carrier absorption of 1550 nm probe signal in Si nanocrystals with excited carriers. Optical 405 nm pump was used to increase free carrier concentration. By applying pulsed pump excitation, -1.55 dB deep intensity modulation was achieved in 5 mm long waveguides. The modulation bandwidth is limited to few kHz due to excited carrier relaxation time (τ ~ 100 μs). Demonstrated all-optical reconfigurable polymer waveguides are a promising potential alternative to thermo-optical switches.
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| 24. |
- Peillod, Alexandre, et al.
(författare)
-
The role of ductile flow of the lower crust in controlling heat advection in the footwall of the Naxos extensional fault system (Aegean Sea, Greece)
-
Tidskriftsartikel (refereegranskat)abstract
- Geothermobarometric and structural work indicates that metamorphism in the footwall of the migmatitic Naxos core complex is strongly coupled to heat advection in the lower crust. Using the average pressure-temperature (P-T) method of THERMOCALC for geothermobarometric calculations coupled with detailed textural work, we constructed P-T paths for nine samples that have different spatial relationships to the Naxos extensional fault system and a migmatite dome in the center of the Naxos core complex. All nine samples show early near isothermal decompression. The late, cooling segment of the P-T paths shows systematic spatial differences in temperature gradients relative to the distance of the samples below the Naxos extensional detachment (representing the top of the Naxos extensional fault system). The differences in late thermal gradients correlate with finite strain, a proxy for the intensity of ductile flow. High finite strain correlates with high thermal gradients that do not change with distance below the Naxos detachment, whereas low finite strain correlates with downward decreasing thermal gradients. The difference in late thermal gradients and finite strain define a thermal asymmetry controlled by ductile flow, which we interpret to show that ductile flow controlled advection of heat and thus high-grade metamorphism on Naxos. We conclude that advective heating is an important driver of metamorphism in extensional settings.
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| 25. |
- Pellegrini, G., et al.
(författare)
-
Technology development of 3D detectors for high-energy physics and imaging
- 2002
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 487:02-jan, s. 19-26
-
Tidskriftsartikel (refereegranskat)abstract
- Various fabrications routes to create '3D' detectors have been investigated and the electrical characteristics of these structures have been compared to simulations. The geometry of the detectors is hexagonal with a central anode surrounded by six cathode contacts. A uniform electric field is obtained with the maximum drift and depletion distance set by electrode spacings rather than detector thickness. This should improve the ability of silicon to operate in the presence of the severe bulk radiation damage expected in high-energy colliders. Moreover, 3D detectors made with other materials (e.g. GaAs, SiC) may be used, for example, in X-ray detection for medical imaging. Holes in the substrate were made either by etching with an inductively coupled plasma machine, by laser drilling or by photochemical etching. A number of different hole diameters and thickness have been investigated. Experimental characteristics have been compared to MEDICI simulations.
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| 26. |
- Pellegrino, P., et al.
(författare)
-
Time-resolved analysis of the white photoluminescence from SiO2 films after Si and C coimplantation
- 2004
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 84:1, s. 25-27
-
Tidskriftsartikel (refereegranskat)abstract
- The analysis of the white photoluminescence (PL) from Si+ and C+ coimplanted SiO2 is reported as a function of the implanted dose. By both steady and time-resolved measurements, the presence of several components in the emission between 2 and 3.3 eV has been resolved. The decays of the PL transients are characterized by short lifetimes, below 2 ns. For the emission at 2.1-2.3 eV, photoluminescence decay transients have been measured, obtaining a fast relaxation component of about 50-70 ps, followed by a slower component of the order of 1 ns. These values contrast with the very slow behavior, characteristic for the light emission from Si nanocrystals, and make carbon-related emitting centers interesting for optoelectronic applications where fast switching behavior is important.
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| 27. |
- Slettengren, M, et al.
(författare)
-
Silicone Oil Decreases Biofilm Formation in a Capacitance-Based Automatic Urine Measurement System
- 2021
-
Ingår i: Sensors (Basel, Switzerland). - : MDPI AG. - 1424-8220. ; 21:2
-
Tidskriftsartikel (refereegranskat)abstract
- Capacitance-based automatic urine measurement is a validated technique already implemented in clinical practice. However, albuminuria and free hemoglobinuria cause progressive biofilm buildup on the capacitance sensors of the urinometers. The aim of this experimental study is to investigate the influence of albumin and free hemoglobin on the capacitance signal of an automatic urinometer with and without the addition of silicone oil. A solution of Ringer’s acetate mixed with either albumin or free hemoglobin was run through an automatic urinometer containing either a water-soluble capsule with silicone oil or not. In total, around 500 capacitance measurements were retrieved from the albumin and free hemoglobin group, respectively. The mean increase in capacitance in the albumin 3 g/L group was 257 ± 100 pF without and 105 ± 30 pF with silicone oil, respectively, during 24 h. After ten hours of recording, differences between the two albumin groups reached statistical significance. For the free hemoglobin groups (0.01 g/L), the mean increase in capacitance was 190 ± 170 pF with silicone oil, and 324 ± 80 pF without, with a significant difference between the groups after 20 h and onwards. Coating of the capacitance measurement membrane of the automatic urinometer by albumin or free hemoglobin was significantly decreased by silicone oil, prolonging the functionality of the device.
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| 28. |
- Sychugov, Ilya, et al.
(författare)
-
Exciton localization in doped Si nanocrystals from single dot spectroscopy studies
- 2012
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 86:7, s. 075311-
-
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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| 29. |
- Sychugov, Ilya, et al.
(författare)
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Luminescent silicon nanocrystals as downconverters for photovoltaic and lighting applications
- 2016
-
Ingår i: Asia Communications and Photonics Conference, ACP. - : OSA - The Optical Society.
-
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. Asia Communications and Photonics Conferene (ACP)
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| 30. |
- Sychugov, Ilya, et al.
(författare)
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Photoluminescence measurements of zero-phonon optical transitions in silicon nanocrystals
- 2011
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 84:12, s. 125326-
-
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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| 31. |
- Sychugov, Ilya, et al.
(författare)
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Probing silicon quantum dots by single-dot techniques
- 2017
-
Ingår i: Nanotechnology. - : Institute of Physics (IOP). - 0957-4484 .- 1361-6528. ; 28:7
-
Tidskriftsartikel (refereegranskat)abstract
- Silicon nanocrystals represent an important class of non-toxic, heavy-metal free quantum dots, where the high natural abundance of silicon is an additional advantage. Successful development in mass-fabrication, starting from porous silicon to recent advances in chemical and plasma synthesis, opens up new possibilities for applications in optoelectronics, bio-imaging, photovoltaics, and sensitizing areas. In this review basic physical properties of silicon nanocrystals revealed by photoluminescence spectroscopy, lifetime, intensity trace and electrical measurements on individual nanoparticles are summarized. The fabrication methods developed for accessing single Si nanocrystals are also reviewed. It is concluded that silicon nanocrystals share many of the properties of direct bandgap nanocrystals exhibiting sharp emission lines at low temperatures, on/off blinking, spectral diffusion etc. An analysis of reported results is provided in comparison with theory and with direct bandgap material quantum dots. In addition, the role of passivation and inherent interface/matrix defects is discussed.
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| 32. |
- Sychugov, Ilya, et al.
(författare)
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Structural imaging of a Si quantum dot: Towards combined PL and TEM characterization
- 2006
-
Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 121:2, s. 353-
-
Tidskriftsartikel (refereegranskat)abstract
- Individual silicon quantum dots were fabricated by electron-beam lithography, plasma etching and a two-step oxidation process. This enables photoluminescence (PL) from individual dots at various temperatures to be detected and spectrally resolved using a sensitive charge-coupled device camera-imaging system, as reported previously. The regular array-like arrangement of oxidized pillars containing individual nanocrystals, in principle, enables combined transmission electron microscopy (TEM) and low-temperature PL characterization of the same Si quantum dot. To this end, a technique employing focused ion beam was developed for preparation of the pillar/nanocrystal of interest for TEM. It is shown that silicon quantum dots of several nanometers in size can be characterized using such a method.
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| 33. |
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| 34. |
- Valenta, J., et al.
(författare)
-
Active planar optical waveguide made from luminescent silicon nanocrystals
- 2003
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 82:6, s. 955-957
-
Tidskriftsartikel (refereegranskat)abstract
- We show experimentally that a layer of silicon nanocrystals, prepared by the Si-ion implantation (with the energy of 400 keV) into a synthetic silica slab and exhibiting room-temperature red photoluminescence, can serve simultaneously as a single-mode planar optical waveguide. The waveguide is shown to self-select guided transverse electric and transverse magnetic modes from the broad photoluminescence emission of the nanocrystals resulting in a substantially narrower emission spectrum for these modes. We further report on an investigation of optical gain in a sample implanted to a dose of 4x10(17) cm(-2). Despite the occurrence of strong waveguiding, results of the variable stripe length method turned out not to be able to give unambiguous evidence for optical gain.
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| 35. |
- Valenta, J., et al.
(författare)
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Colloidal suspensions of silicon nanocrystals : from single nanocrystals to photonic structures
- 2005
-
Ingår i: Optical materials (Amsterdam). - : Elsevier BV. - 0925-3467 .- 1873-1252. ; 27:5, s. 1046-1049
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal suspesions of Si nanocrystals (NCs) are prepared from light-emitting porous Si grains obtained by mechanical pulverization of electrochemically etched layers. Sedimented and/or filtered Si NCs sols reveal a green photoluminescence (PL) band around 530nm, which is interpreted as radiative recombination of electron-hole pairs inside Si NCs with diameter about 2nm. These colloidal solutions have multiple advantages for both fundamental investigations and for nanotechnology. In one extreme, single molecule spectroscopy techniques can be applied to investigate PL of single grains of Si NCs dispersed on substrates from highly diluted solutions. On the other hand, concentrated suspensions enable us to fabricate bulk samples with embedded Si NCs or to prepare self-organised nanostructures on surfaces.
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| 36. |
- Valenta, J., et al.
(författare)
-
Electroluminescence microscopy and spectroscopy of silicon nanocrystals in thin SiO2 layers
- 2001
-
Ingår i: Optical materials (Amsterdam). - 0925-3467 .- 1873-1252. ; 17:02-jan, s. 45-50
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Tidskriftsartikel (refereegranskat)abstract
- Stable continuously operable electroluminescent diodes have been fabricated by Sii-ion implantation and annealing of thin SiO2 layers on a silicon substrate. The external quantum efficiency of the device is reaching 3 x 10(-5) for the best diodes. Electroluminescence (EL) emission band is wide and centered at 800 nm. EL is due to radiative recombination of tunneling carriers in Si-nanocrystals(NC) with small contribution of oxide defects (peak at 650 nm). EL images reveal inhomogeneous emission structures on the micrometer scale. Mainly, a small number of bright spots with diffraction limited size (similar to 600 nm) with a homogeneous background are observed and their EL spectra measured using an imaging spectrometer with a liquid-nitrogen-cooled CCD camera. The bright EL spots originate from the efficiently excited emission of oxide defects and/or emission of a few (possibly single) Si-NC, most likely at places with locally increased current. The low efficiency is probably a consequence of current tunneling through optically inactive nanocrystals or defects in a very thin oxide layer.
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| 37. |
- Valenta, J., et al.
(författare)
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Microcavity-like leaky mode emission from a planar optical waveguide made of luminescent silicon nanocrystals
- 2004
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 96:9, s. 5222-5225
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Tidskriftsartikel (refereegranskat)abstract
- The propagation of light emitted from silicon nanocrystals forming planar waveguides buried in SiO2 is studied both experimentally and theoretically. Experiments reveal that photoluminescence spectra detected from the sample facet mainly contains narrow (10-20 nm full-with-at-half-maximum) polarization-resolved transverse electric and transverse magnetic modes instead of the usual broad nanocrystal emission band peaked at 700-800 nm. A theoretical model developed in the framework of wave optics identifies these modes as substrate modes propagating along the waveguide boundary (not the usual modes guided inside the nanocrystal plane due to its graded index profile). This peculiar observation is the consequence of the high losses in the nanocrystalline waveguide and may occur in other dissipative waveguide structures under conditions that are discussed.
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| 38. |
- Valenta, J., et al.
(författare)
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Optical spectroscopy of individual silicon nanocrystals
- 2008
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Ingår i: Silicon Nanophotonics: Basic Principles, Current Status and Perspectives. - : Pan Stanford Publishing. - 9789814241113 ; , s. 179-209
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The available data on photoluminescence (PL) spectroscopy of single Si nanocrystals (Si-nc) is reviewed for two types of samples: (i) Regular matrices of Si pillars produced by electron-beam lithography, reactive ion etching and oxidation, (ii) grains of porous Si deposited onto a substrate from a diluted colloidal suspension. A wide-field imaging micro-spectroscope with detection by a CCD camera is used preferably to detect spectra, while a confocal microscope with singlephoton- counting detection is applied for detection of PL fluctuations, so called ON-OFF blinking. Cryogenic-temperature PL spectroscopy of Si-nc reveals atomic-like narrow lines that document an unexpectedly large contribution of zero-phonon transitions and also some lowfrequency phonon-replicas. The blinking photon-statistics indicates that the transition between bright and dark states of a Si-nc has character of a diffusion-controlled electron-transfer reaction where quenching occurs by Auger recombination. Finally we show that all published results indicate a common PL mechanism of Si-nc, largely insensitive to fabrication methods.
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| 39. |
- Valenta, J., et al.
(författare)
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Waveguiding effects in the measurement of optical gain in a layer of Si nanocrystals
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:8, s. 1396-1398
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Tidskriftsartikel (refereegranskat)abstract
- We discuss applicability of the variable stripe length method to experimental investigation of optical gain in a luminescent layer that behaves like a planar waveguide. We show that an interplay between the output direction of guided light modes and the numerical aperture of the collection optics may lead to an artifact manifesting itself as an apparent but false gain. We propose a way to circumvent this inconvenience by using a shifting excitation spot complementary measurement. The method is demonstrated on a layer of Si nanocrystals embedded into a synthetic silica plate.
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