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Seong-ju Park - One of the best experts on this subject based on the ideXlab platform.
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Enhanced quantum confinement in tensile-strained Silicon Nanocrystals embedded in Silicon nitride
Current Applied Physics, 2017Co-Authors: Chang-hee Cho, Jang-won Kang, Il-kyu Park, Seong-ju ParkAbstract:Abstract Here, we report that the tensile strain in Silicon Nanocrystals embedded in Silicon nitride significantly changes the size-dependent evolution of the conduction and valence energy levels, compared with strain-free Silicon Nanocrystals. Using capacitance spectroscopy, the quantum-confined energy shifts in the conduction and valence levels were identified as ΔE C (eV) = 11.7 /d 2 , and ΔE V (eV) = −4.5 /d 2 , where d is the mean diameter of the Silicon Nanocrystals in nanometers. These findings indicated that the tensile strain in the Silicon Nanocrystals significantly increased the quantum confinement, by a factor of 3.3 in the conduction levels, and by a factor of 1.8 in the valence levels.
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Characterization of electronic structure of Silicon Nanocrystals in Silicon nitride by capacitance spectroscopy
Applied Physics Letters, 2010Co-Authors: Chang-hee Cho, Sang Kyun Kim, Baek Hyun Kim, Seong-ju ParkAbstract:The electronic structure of Silicon Nanocrystals embedded in a Silicon nitride insulating film is identified by using a capacitance spectroscopy. The tunneling capacitor device, which is used in this study, consists of a tunneling Silicon nitride, an array of Silicon Nanocrystals embedded in a Silicon nitride film, and a blocking Silicon nitride deposited on p-type (100) Si substrate. The absolute position of the lowest conduction and the highest valence levels of the Silicon nanocrystal is revealed and the band-gap energy of Silicon Nanocrystals estimated by the capacitance spectroscopy agrees well with that measured by photoluminescence spectroscopy.The electronic structure of Silicon Nanocrystals embedded in a Silicon nitride insulating film is identified by using a capacitance spectroscopy. The tunneling capacitor device, which is used in this study, consists of a tunneling Silicon nitride, an array of Silicon Nanocrystals embedded in a Silicon nitride film, and a blocking Silicon nitride deposited on p-type (100) Si substrate. The absolute position of the lowest conduction and the highest valence levels of the Silicon nanocrystal is revealed and the band-gap energy of Silicon Nanocrystals estimated by the capacitance spectroscopy agrees well with that measured by photoluminescence spectroscopy.
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Strong size-dependent characteristics of carrier injection in quantum-confined Silicon Nanocrystals
Applied Physics Letters, 2009Co-Authors: Chang-hee Cho, Sang Kyun Kim, Baek Hyun Kim, Seong-ju ParkAbstract:We report the strong size-dependent carrier injection process in quantum-confined Silicon Nanocrystals embedded in Silicon nitride films. As the diameter of Silicon Nanocrystals increases, the threshold voltage for carrier injection decreases whereas the number of injected carriers increases due to the quantum size effect. The tunneling time for the carrier injection is decreased by two orders of magnitude when the diameter of Silicon Nanocrystals is increased from 3.4 to 5.0 nm, and this is attributed to the enhanced nonresonant tunneling in the larger Silicon Nanocrystals.
Chang-hee Cho - One of the best experts on this subject based on the ideXlab platform.
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Enhanced quantum confinement in tensile-strained Silicon Nanocrystals embedded in Silicon nitride
Current Applied Physics, 2017Co-Authors: Chang-hee Cho, Jang-won Kang, Il-kyu Park, Seong-ju ParkAbstract:Abstract Here, we report that the tensile strain in Silicon Nanocrystals embedded in Silicon nitride significantly changes the size-dependent evolution of the conduction and valence energy levels, compared with strain-free Silicon Nanocrystals. Using capacitance spectroscopy, the quantum-confined energy shifts in the conduction and valence levels were identified as ΔE C (eV) = 11.7 /d 2 , and ΔE V (eV) = −4.5 /d 2 , where d is the mean diameter of the Silicon Nanocrystals in nanometers. These findings indicated that the tensile strain in the Silicon Nanocrystals significantly increased the quantum confinement, by a factor of 3.3 in the conduction levels, and by a factor of 1.8 in the valence levels.
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Characterization of electronic structure of Silicon Nanocrystals in Silicon nitride by capacitance spectroscopy
Applied Physics Letters, 2010Co-Authors: Chang-hee Cho, Sang Kyun Kim, Baek Hyun Kim, Seong-ju ParkAbstract:The electronic structure of Silicon Nanocrystals embedded in a Silicon nitride insulating film is identified by using a capacitance spectroscopy. The tunneling capacitor device, which is used in this study, consists of a tunneling Silicon nitride, an array of Silicon Nanocrystals embedded in a Silicon nitride film, and a blocking Silicon nitride deposited on p-type (100) Si substrate. The absolute position of the lowest conduction and the highest valence levels of the Silicon nanocrystal is revealed and the band-gap energy of Silicon Nanocrystals estimated by the capacitance spectroscopy agrees well with that measured by photoluminescence spectroscopy.The electronic structure of Silicon Nanocrystals embedded in a Silicon nitride insulating film is identified by using a capacitance spectroscopy. The tunneling capacitor device, which is used in this study, consists of a tunneling Silicon nitride, an array of Silicon Nanocrystals embedded in a Silicon nitride film, and a blocking Silicon nitride deposited on p-type (100) Si substrate. The absolute position of the lowest conduction and the highest valence levels of the Silicon nanocrystal is revealed and the band-gap energy of Silicon Nanocrystals estimated by the capacitance spectroscopy agrees well with that measured by photoluminescence spectroscopy.
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Strong size-dependent characteristics of carrier injection in quantum-confined Silicon Nanocrystals
Applied Physics Letters, 2009Co-Authors: Chang-hee Cho, Sang Kyun Kim, Baek Hyun Kim, Seong-ju ParkAbstract:We report the strong size-dependent carrier injection process in quantum-confined Silicon Nanocrystals embedded in Silicon nitride films. As the diameter of Silicon Nanocrystals increases, the threshold voltage for carrier injection decreases whereas the number of injected carriers increases due to the quantum size effect. The tunneling time for the carrier injection is decreased by two orders of magnitude when the diameter of Silicon Nanocrystals is increased from 3.4 to 5.0 nm, and this is attributed to the enhanced nonresonant tunneling in the larger Silicon Nanocrystals.
Uwe R. Kortshagen - One of the best experts on this subject based on the ideXlab platform.
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Aerosol-Phase Synthesis and Processing of Luminescent Silicon Nanocrystals
Chemistry of Materials, 2019Co-Authors: Uwe R. KortshagenAbstract:Silicon quantum dots are attractive materials for luminescent devices and bioimaging applications. For these light-emitting applications, higher photoluminescence efficiency is desired in order to achieve better device performance. Nonthermal plasma synthesis successfully allows for the continuous production of Silicon Nanocrystals, but postprocessing is necessary to improve photoluminescence quantum yields so that Nanocrystals can be used for luminescence applications. In this work, we demonstrate an all-aerosol-phase synthesis and processing route that integrates nonthermal plasma synthesis, plasma-assisted surface functionalization with alkene ligands, and in-flight annealing within one flow stream. Here, luminescent Silicon Nanocrystals are synthesized and postprocessed on a time scale of only 100 ms, which is orders of magnitude faster than previous synthesis and functionalization schemes. The as-produced Silicon Nanocrystals have photoluminescence quantum yields exceeding 20%, which is a 5-fold incr...
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Toxicity Evaluation of Boron- and Phosphorus-Doped Silicon Nanocrystals toward Shewanella oneidensis MR-1
ACS Applied Nano Materials, 2018Co-Authors: Bo Zhi, Uwe R. Kortshagen, Sadhana Mishra, Natalie V. Hudson-smith, Christy L. HaynesAbstract:Silicon Nanocrystals, also known as Silicon quantum dots, are regarded as green alternatives to traditional quantum dots composed of heavy metal elements. While it is well-known that the semiconductor properties of these materials can be tuned by doping with p/n-type dopants (i.e., boron and phosphorus), there is a lack of systematic understanding of their potential environmental impact if released into the ecosystem. Here, we demonstrate that introduction of dopants, especially phosphorus, cause doped Silicon Nanocrystals to produce reactive oxygen species, resulting in significant toxicity to a model microorganism, Shewanella oneidensis MR-1. In addition, the interaction between bacteria cells and Silicon Nanocrystals was investigated using dark field microscopy and bio-TEM. Interestingly, boron-doped Silicon Nanocrystals tended to attach to the cell surface while this phenomenon was not observed for undoped or phosphorus-doped Silicon Nanocrystals.
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Plasmonic Properties of Silicon Nanocrystals Doped with Boron and Phosphorus
Nano letters, 2015Co-Authors: Nicolaas J. Kramer, Katelyn S. Schramke, Uwe R. KortshagenAbstract:Degenerately doped Silicon Nanocrystals are appealing plasmonic materials due to Silicon’s low cost and low toxicity. While surface plasmonic resonances of boron-doped and phosphorus-doped Silicon Nanocrystals were recently observed, there currently is poor understanding of the effect of surface conditions on their plasmonic behavior. Here, we demonstrate that phosphorus-doped Silicon Nanocrystals exhibit a plasmon resonance immediately after their synthesis but may lose their plasmonic response with oxidation. In contrast, boron-doped Nanocrystals initially do not exhibit plasmonic response but become plasmonically active through postsynthesis oxidation or annealing. We interpret these results in terms of substitutional doping being the dominant doping mechanism for phosphorus-doped Silicon Nanocrystals, with oxidation-induced defects trapping free electrons. The behavior of boron-doped Silicon Nanocrystals is more consistent with a strong contribution of surface doping. Importantly, boron-doped Silicon ...
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phosphorus doped Silicon Nanocrystals exhibiting mid infrared localized surface plasmon resonance
Nano Letters, 2013Co-Authors: David J Rowe, Jong Seok Jeong, Andre K Mkhoyan, Uwe R. KortshagenAbstract:Localized surface plasmon resonances (LSPRs) enable tailoring of the optical response of nanomaterials through their free carrier concentration, morphology, and dielectric environment. Recent efforts to expand the spectral range of usable LSPR frequencies into the infrared successfully demonstrated LSPRs in doped semiconductor Nanocrystals. Despite Silicon’s importance for electronic and photonic applications, no LSPRs have been reported for doped Silicon Nanocrystals. Here we demonstrate doped Silicon Nanocrystals synthesized via a nonthermal plasma technique that exhibits tunable LSPRs in the energy range of 0.07–0.3 eV or mid-infrared wavenumbers of 600–2500 cm–1.
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SF6 plasma etching of Silicon Nanocrystals
Nanotechnology, 2008Co-Authors: R. W. Liptak, Uwe R. Kortshagen, Brent M. Devetter, J. H. Thomas, Stephen A. CampbellAbstract:An SF6-based plasma has been employed to perform in-flight etching of Silicon Nanocrystals (Si-NCs) after they were synthesized in an SiH4-based plasma. The photoluminescence of the Si-NCs blue-shifts after etching, indicating an etching-induced size reduction of the Si-NCs. It is shown that both the SF6 plasma power and the flow rate can be utilized to control the etch rate (and thus the size reduction) of the Si-NCs. The SF6 etched Si-NCs show only low concentrations of residual impurities other than fluorine. Quantum yields as high as 50% have been observed from these SF6 etched Si-NCs despite oxidation.
Geoffrey A. Ozin - One of the best experts on this subject based on the ideXlab platform.
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Silicon Nanocrystals: It's Simply a Matter of Size
ChemNanoMat, 2016Co-Authors: Wei Sun, Chenxi Qian, Kenneth K. Chen, Geoffrey A. OzinAbstract:Composed of one of the most earth abundant, low cost and least toxic elements, Silicon Nanocrystals exhibit quantum and spatial confinement effects when their size is diminished to that of the exciton, around 5 nm. With the recent discovery of various means for synthesizing and separating Silicon Nanocrystals into narrow size distribution mono-dispersions, it became possible for the first time to implement more deeply analytical studies of their size-dependent chemical, physical and biological properties than was possible with poly-dispersions. In this article we take a look at some recent studies of mono-dispersions of Silicon Nanocrystals where it is apparent that size really matters. With this newfound knowledge we imagine the new directions that the field may take in the future. The topics covered include how Silicon nanocrystal size is manifest on their (i) surface structure and reactivity, (ii) optical and electronic properties, (iii) chemical and photochemical stability, and (iv) biochemical and cytotoxicity behavior. The article concludes with a vision of what the future might hold for this important class of Nanocrystals.
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Silicon monoxide a convenient precursor for large scale synthesis of near infrared emitting monodisperse Silicon Nanocrystals
Nanoscale, 2016Co-Authors: Chenxi Qian, Liwei Wang, Gilberto Casillas, Amr S Helmy, Geoffrey A. OzinAbstract:While Silicon Nanocrystals (ncSi) embedded in Silicon dioxide thin films have been intensively studied in physics, the potential of batch synthesis of Silicon Nanocrystals from the solid-state disproportionation of SiO powder has not drawn much attention in chemistry. Herein we describe some remarkable effects observed in the diffraction, microscopy and spectroscopy of SiO powder upon thermal processing in the temperature range 850–1100 °C. Quantum confinement effects and structural changes of the material related to the size of the Silicon Nanocrystals nucleated and grown in this way were established by Photoluminescence (PL), Raman, FTIR and UV-Visible spectroscopy, PXRD and STEM, pinpointing that the most significant disproportionation transformations happened in the temperature range between 900 and 950 °C. With this know-how a high yield synthesis was developed that produced polydispersions of decyl-capped, hexane-soluble Silicon Nanocrystals predominantly with near infrared (NIR) PL. Using size-selective precipitation, these polydispersions were separated into monodisperse fractions, which allowed their PL absolute quantum yield (AQY) to be studied as a function of Silicon nanocrystal size. This investigation yielded volcano-shaped plots for the AQY confirming the most efficient PL wavelength for ncSi to be located at around 820–830 nm, which corresponded to a size of 3.5–4.0 nm. This work provides opportunities for applications of size-selected near infrared emitting Silicon Nanocrystals in biomedical imaging and photothermal therapy.
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switching on quantum size effects in Silicon Nanocrystals
Advanced Materials, 2015Co-Authors: Wei Sun, Chenxi Qian, Melanie L. Mastronardi, Muan Wei, Liwei Wang, Gilberto Casillas, Josef Breu, Geoffrey A. OzinAbstract:The size-dependence of the absolute luminescence quantum yield of size-separated Silicon Nanocrystals reveals a "volcano" behavior, which switches on around 5 nm, peaks at near 3.7-3.9 nm, and decreases thereafter. These three regions respectively define: i) the transition from bulk to strongly quantum confined emissive Silicon, ii) increasing confinement enhancing radiative recombination, and iii) increasing contributions favoring non-radiative recombination.
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Hydrosilylation kinetics of Silicon Nanocrystals.
Chemical communications (Cambridge England), 2013Co-Authors: Wei Sun, Chenxi Qian, Melanie L. Mastronardi, Muan Wei, Geoffrey A. OzinAbstract:Hydrosilylation kinetics of hydride-capped Silicon Nanocrystals with 1-decene are reported for the first time. In a side-by-side comparison, it is found that microwave heating has no evident acceleration effect on the hydrosilylation rate relative to conventional thermal heating.
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size dependent absolute quantum yields for size separated colloidally stable Silicon Nanocrystals
Nano Letters, 2012Co-Authors: Melanie L. Mastronardi, Florian Maierflaig, Daniel Faulkner, Eric J Henderson, Christian Kubel, Uli Lemmer, Geoffrey A. OzinAbstract:Size-selective precipitation was used to successfully separate colloidally stable allylbenzene-capped Silicon Nanocrystals into several visible emitting monodisperse fractions traversing the quantum size effect range of 1–5 nm. This enabled the measurement of the absolute quantum yield and lifetime of photoluminescence of allylbenzene-capped Silicon Nanocrystals as a function of size. The absolute quantum yield and lifetime are found to monotonically decrease with decreasing nanocrystal size, which implies that nonradiative vibrational and surface defect effects overwhelm spatial confinement effects that favor radiative relaxation. Visible emission absolute quantum yields as high as 43% speak well for the development of “green” Silicon nanocrystal color-tunable light emitting diodes that can potentially match the performance of their toxic heavy metal chalcogenide counterparts.
Margit Zacharias - One of the best experts on this subject based on the ideXlab platform.
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atom probe tomography of size controlled phosphorus doped Silicon Nanocrystals
Physica Status Solidi-rapid Research Letters, 2017Co-Authors: Keita Nomoto, Margit Zacharias, Gavin Conibeer, Daniel Hiller, S Gutsch, Anna V Ceguerra, Andrew J Breen, Ivan Perezwurfl, Simon P RingerAbstract:Doping of Silicon Nanocrystals is essential to control their electronic and optical properties. The incorporation of an impurity into a Silicon nanovolume is a nontrivial task due to the self-purification effect. Here, a systematic atom probe tomography study of the phosphorus distribution and incorporation in size-controlled Silicon Nanocrystals embedded in Silicon dioxide is presented. Qualitatively, it turns out that the phosphorus distribution in the system follows a universal, nanocrystal-size independent trend: phosphorus-enrichment at the interface with a substantial phosphorus-incorporation in the Silicon nanocrystal as small as 2 nm in diameter. This clearly contradicts strict self-purification. These observations are explained by the bulk-solubility and -segregation behaviour, kinetic effects related to the diffusion lengths, and nanoscale interface strain. The quantitative determination of the amount of phosphorus atoms per quantum dot enables a systematic understanding of phosphorus-induced effects on optical and electronic properties of Silicon nanovolumes.
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Doping efficiency of phosphorus doped Silicon Nanocrystals embedded in a SiO2 matrix
Applied Physics Letters, 2012Co-Authors: Sebastian Gutsch, A. M. Hartel, Daniel Hiller, Nikolai Zakharov, Peter Werner, Margit ZachariasAbstract:Strongly size controlled Silicon Nanocrystals in Silicon oxynitride matrix were prepared using plasma enhanced chemical vapor deposition following the superlattice approach. Doping was achieved by adding diluted phosphine as a precursor gas. Phosphorus quantification was done by secondary ion mass spectrometry. A model based on Poissonian distributions of interface defects and dopants is proposed to calculate the defects and the dopants per Silicon nanocrystal as a function of phosphorus concentration. The model requires the comparison between the photoluminescence spectra from passivated and unpassivated samples. Finally, the doping efficiency of Silicon Nanocrystals embedded in Silicon oxynitride is estimated to be >20%.
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Silicon Nanocrystals: Size Matters
Advanced Materials, 2005Co-Authors: J. Heitmann, Margit Zacharias, Frank Müller, Ulrich GöseleAbstract:This paper reviews new approaches to size-controlled Silicon-nanocrystal synthesis. These approaches allow narrowing of the size distribution of the Nanocrystals compared with those obtained by conventional synthesis processes such as ion implantation into SiO 2 or phase separation of sub-stoichiometric SiO x layers. This size control is realized by different approaches to introducing a superlattice-like structure into the synthesis process, by velocity selection of Silicon aerosols, or by the use of electron lithography and subsequent oxidation processes. Nanocrystals between 2 and 20 nm in size with a full width at half maximum of the size distribution of 1 nm can be synthesized and area densities above 10 1 2 cm - 2 can be achieved. The role of surface passivation is elucidated by comparing Si/SiO 2 layers with superlattices of fully passivated Silicon Nanocrystals within a SiO 2 matrix. The demands on Silicon Nanocrystals for various applications such as non-volatile memories or light-emitting devices are discussed for different size-controlled nanocrystal synthesis approaches.
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Optical gain in monodispersed Silicon Nanocrystals
Journal of Applied Physics, 2004Co-Authors: Massimo Cazzanelli, Lorenzo Pavesi, Daniel Navarro-urrios, Francesco Riboli, Nicola Daldosso, J. Heitmann, R. Scholz, Margit Zacharias, Ulrich GöseleAbstract:Stimulated emission from Silicon-nanocrystal planar waveguides grown via phase separation and thermal crystallization of SiO∕SiO2 superlattices is presented. Under high power pulsed excitation, positive optical gain can be observed once a good optical confinement in the waveguide is achieved and the Silicon Nanocrystals have proper size. A critical tradeoff between Auger nonradiative recombination processes and stimulated emission is observed. The measured large gain values are explained by the small size dispersion in these Silicon Nanocrystals.
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Photoluminescence of Er 3+ Ions in Layers of Quasi-Ordered Silicon Nanocrystals in a Silicon Dioxide Matrix
Journal of Experimental and Theoretical Physics, 2003Co-Authors: Pavel K. Kashkarov, V. Yu. Timoshenko, J. Heitmann, O. A. Shalygina, M. G. Lisachenko, B. V. Kamenev, Michael W. I. Schmidt, Margit ZachariasAbstract:The spectra and kinetics of photoluminescence from multilayered structures of quasi-ordered Silicon Nanocrystals in a silica matrix were studied for undoped samples and samples doped with erbium. It was shown that the optical excitation energy of Silicon Nanocrystals could be effectively transferred to Er3+ ions, which was followed by luminescence at a wavelength of 1.5 µm. The effectiveness of energy transfer increased as the size of Silicon Nanocrystals decreased and the energy of exciting light quanta increased. The excitation of erbium luminescence in the structures was explained based on dipole-dipole interaction (the Forster mechanism) between excitons in Silicon Nanocrystals and Er3+ ions in silica surrounding them.
