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Christophe David - One of the best experts on this subject based on the ideXlab platform.
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Quantum Confinement effects in Pb nanocrystals grown on InAs
Physical Review B, 2018Co-Authors: Tianzhen Zhang, Sergio Vlaic, Stéphane Pons, Alexandre Assouline, Alexandre Zimmers, Dimitri Roditchev, Hervé Aubin, Guy Allan, Christophe Delerue, Christophe DavidAbstract:In the recent work of Ref.\cite{Vlaic2017-bs}, it has been shown that Pb nanocrystals grown on the electron accumulation layer at the (110) surface of InAs are in the regime of Coulomb blockade. This enabled the first scanning tunneling spectroscopy study of the superconducting parity effect across the Anderson limit. The nature of the tunnel barrier between the nanocrystals and the substrate has been attributed to a Quantum constriction of the electronic wave-function at the interface due to the large Fermi wavelength of the electron accumulation layer in InAs. In this manuscript, we detail and review the arguments leading to this conclusion. Furthermore, we show that, thanks to this highly clean tunnel barrier, this system is remarkably suited for the study of discrete electronic levels induced by Quantum Confinement effects in the Pb nanocrystals. We identified three distinct regimes of Quantum Confinement. For the largest nanocrystals, Quantum Confinement effects appear through the formation of Quantum well states regularly organized in energy and in space. For the smallest nanocrystals, only atomic-like electronic levels separated by a large energy scale are observed. Finally, in the intermediate size regime, discrete electronic levels associated to electronic wave-functions with a random spatial structure are observed, as expected from Random Matrix Theory.
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Quantum Confinement effects in Pb nanocrystals grown on InAs
Physical Review B: Condensed Matter and Materials Physics, 2018Co-Authors: Tianzhen Zhang, Sergio Vlaic, Stéphane Pons, Alexandre Assouline, Alexandre Zimmers, Dimitri Roditchev, Hervé Aubin, Guy Allan, Christophe Delerue, Christophe DavidAbstract:In the recent work of Vlaic et al. [Nat. Commun. 8, 14549 (2017)], it has been shown that Pb nanocrystals grown on the electron accumulation layer at the (110) surface of InAs are in the regime of Coulomb blockade. This enabled a scanning tunneling spectroscopy study of the superconducting parity effect across the Anderson limit. The nature of the tunnel barrier between the nanocrystals and the substrate has been attributed to a Quantum constriction of the electronic wave function at the interface due to the large Fermi wavelength of the electron accumulation layer in InAs. In this paper, we detail and review the arguments leading to this conclusion. Furthermore, we show that, thanks to this highly clean tunnel barrier, this system is remarkably suited for the study of discrete electronic levels induced by Quantum Confinement effects in the Pb nanocrystals. We identified three distinct regimes of Quantum Confinement. For the largest nanocrystals, Quantum Confinement effects appear through the formation of Quantum well states regularly organized in energy and in space. For the smallest nanocrystals, only atomiclike electronic levels separated by a large energy scale are observed. Finally, in the intermediate size regime, discrete electronic levels associated to electronic wave functions with a random spatial structure are observed, as expected from random matrix theory.
David J. Lockwood - One of the best experts on this subject based on the ideXlab platform.
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Quantum Confinement in Si and Ge nanostructures
Journal of Applied Physics, 2012Co-Authors: E. G. Barbagiovanni, David J. Lockwood, Peter J. Simpson, Lyudmila V. GoncharovaAbstract:We apply perturbative effective mass theory as a broadly applicable theoretical model for Quantum Confinement (QC) in all Si and Genanostructures including Quantum wells(QWs), wires (Q-wires), and dots(QDs). Within the limits of strong, medium, and weak QC, valence and conduction band edge energy levels (VBM and CBM) were calculated as a function of QD diameters, QW thicknesses, and Q-wire diameters. Crystalline and amorphous Quantum systems were considered separately. Calculated band edge levels with strong, medium, and weak QC models were compared with experimental VBM and CBM reported from X-ray photoemission spectroscopy (XPS), X-ray absorption spectroscopy (XAS), or photoluminescence(PL). Experimentally, the dimensions of the nanostructures were determined directly, by transmission electron microscopy(TEM), or indirectly, by x-ray diffraction (XRD) or by XPS. We found that crystalline materials are best described by a medium Confinement model, while amorphous materials exhibit strong Confinement regardless of the dimensionality of the system. Our results indicate that spatial delocalization of the hole in amorphous versus crystalline nanostructures is the important parameter determining the magnitude of the band gap expansion, or the strength of the Quantum Confinement. In addition, the effective masses of the electron and hole are discussed as a function of crystallinity and spatial Confinement.
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Quantum Confinement in Nanocrystalline Superlattices
MRS Proceedings, 1999Co-Authors: G. F. Grom, Philippe M. Fauchet, Leonid Tsybeskov, John P. Mccaffrey, H. J. Labbé, David J. LockwoodAbstract:ABSTRACTPhotoconductance spectroscopy was used to probe the effects of Quantum Confinement in nanocrystalline (nc)-Si/amorphous (a)-SiO2 superlattices (SLs). A Metal-Oxide-Semiconductor (MOS)-like structure with the nc-Si SL incorporated in the oxide was fabricated to study charging/discharging processes in Si nanocrystals. The fine structure observed in photoconductance spectra at low temperatures was interpreted in terms of singularities in the carrier density of states, possibly due to energy quantization. In addition, a low-resistance sample exhibited photocurrent oscillations with a frequency of several kHz, which could be a manifestation of sequential resonant carrier tunneling in the nc-Si/a-SiO2 SL.
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Quantum Confinement and light emission in sio 2 si superlattices
Nature, 1995Co-Authors: David J. Lockwood, J M BaribeauAbstract:PHOTONIC devices are becoming increasingly important in information and communication technologies. But attempts to integrate photonics with silicon-based microelectronics are hampered by the fact that silicon has an indirect band gap, which prevents efficient electron-photon energy conversion. Light-emitting silicon-based materials have been made using band-structure engineering of SiGe and SiC alloys and Si/Ge superlattices, and by exploiting Quantum-Confinement effects in nanoscale particles and crystallites1–3. The discovery4,5 that silicon can be etched electrochemically into a highly porous form that emits light with a high Quantum yield has opened up the latter approach to intensive study6–12. Here we report the fabrication, by molecular-beam epitaxy, of well-defined superlattices of silicon and SiO2, which emit visible light through photoluminescence. We show that this light emission can be explained in terms of Quantum Confinement of electrons in the two-dimensional silicon layers. These superlattice structures are robust and compatible with standard silicon technology.
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Quantum Confinement induced photoluminescence in porous silicon
Solid State Communications, 1995Co-Authors: David J. Lockwood, Ai Guo WangAbstract:Abstract An investigation of the red photoluminescence (PL) in uniform layers of porous silicon has revealed an inverse relationship between the PL peak energy and the nanoparticle diameter that is in accord with a Quantum Confinement mechanism. The PL energy lies below that of the optical absorption gap in such samples and the theoretical predictions for Quantum dots. It appears that the light emission in porous Si is multiphoton assisted for even quite small nanoparticle sizes.
Guy Allan - One of the best experts on this subject based on the ideXlab platform.
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Quantum Confinement effects in Pb nanocrystals grown on InAs
Physical Review B, 2018Co-Authors: Tianzhen Zhang, Sergio Vlaic, Stéphane Pons, Alexandre Assouline, Alexandre Zimmers, Dimitri Roditchev, Hervé Aubin, Guy Allan, Christophe Delerue, Christophe DavidAbstract:In the recent work of Ref.\cite{Vlaic2017-bs}, it has been shown that Pb nanocrystals grown on the electron accumulation layer at the (110) surface of InAs are in the regime of Coulomb blockade. This enabled the first scanning tunneling spectroscopy study of the superconducting parity effect across the Anderson limit. The nature of the tunnel barrier between the nanocrystals and the substrate has been attributed to a Quantum constriction of the electronic wave-function at the interface due to the large Fermi wavelength of the electron accumulation layer in InAs. In this manuscript, we detail and review the arguments leading to this conclusion. Furthermore, we show that, thanks to this highly clean tunnel barrier, this system is remarkably suited for the study of discrete electronic levels induced by Quantum Confinement effects in the Pb nanocrystals. We identified three distinct regimes of Quantum Confinement. For the largest nanocrystals, Quantum Confinement effects appear through the formation of Quantum well states regularly organized in energy and in space. For the smallest nanocrystals, only atomic-like electronic levels separated by a large energy scale are observed. Finally, in the intermediate size regime, discrete electronic levels associated to electronic wave-functions with a random spatial structure are observed, as expected from Random Matrix Theory.
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Quantum Confinement effects in Pb nanocrystals grown on InAs
Physical Review B: Condensed Matter and Materials Physics, 2018Co-Authors: Tianzhen Zhang, Sergio Vlaic, Stéphane Pons, Alexandre Assouline, Alexandre Zimmers, Dimitri Roditchev, Hervé Aubin, Guy Allan, Christophe Delerue, Christophe DavidAbstract:In the recent work of Vlaic et al. [Nat. Commun. 8, 14549 (2017)], it has been shown that Pb nanocrystals grown on the electron accumulation layer at the (110) surface of InAs are in the regime of Coulomb blockade. This enabled a scanning tunneling spectroscopy study of the superconducting parity effect across the Anderson limit. The nature of the tunnel barrier between the nanocrystals and the substrate has been attributed to a Quantum constriction of the electronic wave function at the interface due to the large Fermi wavelength of the electron accumulation layer in InAs. In this paper, we detail and review the arguments leading to this conclusion. Furthermore, we show that, thanks to this highly clean tunnel barrier, this system is remarkably suited for the study of discrete electronic levels induced by Quantum Confinement effects in the Pb nanocrystals. We identified three distinct regimes of Quantum Confinement. For the largest nanocrystals, Quantum Confinement effects appear through the formation of Quantum well states regularly organized in energy and in space. For the smallest nanocrystals, only atomiclike electronic levels separated by a large energy scale are observed. Finally, in the intermediate size regime, discrete electronic levels associated to electronic wave functions with a random spatial structure are observed, as expected from random matrix theory.
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Quantum Confinement in the Si-III (BC-8) phase of porous silicon
Applied Physics Letters, 1997Co-Authors: Guy Allan, Christophe Delerue, Michel LannooAbstract:Porous silicon was recently shown to give rise to the same semimetallic Si-III (BC-8) phase as silicon upon application and release of high pressure. This phase is known to have a direct gap and we examine the effect of Quantum Confinement on its electronic structure. This is performed by combining empirical tight binding and ab initio local density calculations. The blue shift is found to be similar to what is obtained for nanocrystallites with the diamond structure and the radiative recombination rate is much larger. Comparison with experiment shows that the observed luminescence is not consistent with the Quantum Confinement hypothesis.
Gustavo M. Dalpian - One of the best experts on this subject based on the ideXlab platform.
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Cobalt-doped ZnO nanocrystals: Quantum Confinement and surface effects from ab initio methods
Physical Chemistry Chemical Physics, 2013Co-Authors: Aline L. Schoenhalz, Gustavo M. DalpianAbstract:Cobalt-doped ZnO nanocrystals were studied through ab initio methods based on the Density Functional Theory. Both Quantum Confinement and surface effects were explicitly taken into account. When only Quantum Confinement effects are considered, Co atoms interact through a superexchange mechanism, stabilizing an antiferromagnetic ground state. Usually, this is the case for high quality nanoparticles with perfect surface saturation. When the surfaces were considered, a strong hybridization between the Co atoms and surfaces was observed, strongly changing their electronic and magnetic properties. Our results indicated that the surfaces might qualitatively change the properties of impurities in semiconductor nanocrystals.
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Surface and Quantum Confinement Effects in ZnO Nanocrystals
The Journal of Physical Chemistry C, 2010Co-Authors: Aline L. Schoenhalz, J. T. Arantes, Adalberto Fazzio, Gustavo M. DalpianAbstract:ZnO nanocrystals are studied using theoretical calculations based on the density functional theory. The two main effects related to the reduced size of the nanocrystals are investigated: Quantum Confinement and a large surface:volume ratio. The effects of Quantum Confinement are studied by saturating the surface dangling bonds of the nanocrystals with hypothetical H atoms. To understand the effects of the surfaces of the nanocrystals, all saturation is removed and the system is relaxed to its minimum energy position. Several different surface motifs are reported, which should be observed experimentally. Spin-polarized calculations are performed in the nonsaturated nanocrystals, leading to different magnetic moments. We propose that this magnetic moment can be responsible for the intrinsic magnetism observed in ZnO nanostructures.
Christophe Delerue - One of the best experts on this subject based on the ideXlab platform.
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Quantum Confinement effects in Pb nanocrystals grown on InAs
Physical Review B, 2018Co-Authors: Tianzhen Zhang, Sergio Vlaic, Stéphane Pons, Alexandre Assouline, Alexandre Zimmers, Dimitri Roditchev, Hervé Aubin, Guy Allan, Christophe Delerue, Christophe DavidAbstract:In the recent work of Ref.\cite{Vlaic2017-bs}, it has been shown that Pb nanocrystals grown on the electron accumulation layer at the (110) surface of InAs are in the regime of Coulomb blockade. This enabled the first scanning tunneling spectroscopy study of the superconducting parity effect across the Anderson limit. The nature of the tunnel barrier between the nanocrystals and the substrate has been attributed to a Quantum constriction of the electronic wave-function at the interface due to the large Fermi wavelength of the electron accumulation layer in InAs. In this manuscript, we detail and review the arguments leading to this conclusion. Furthermore, we show that, thanks to this highly clean tunnel barrier, this system is remarkably suited for the study of discrete electronic levels induced by Quantum Confinement effects in the Pb nanocrystals. We identified three distinct regimes of Quantum Confinement. For the largest nanocrystals, Quantum Confinement effects appear through the formation of Quantum well states regularly organized in energy and in space. For the smallest nanocrystals, only atomic-like electronic levels separated by a large energy scale are observed. Finally, in the intermediate size regime, discrete electronic levels associated to electronic wave-functions with a random spatial structure are observed, as expected from Random Matrix Theory.
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Quantum Confinement effects in Pb nanocrystals grown on InAs
Physical Review B: Condensed Matter and Materials Physics, 2018Co-Authors: Tianzhen Zhang, Sergio Vlaic, Stéphane Pons, Alexandre Assouline, Alexandre Zimmers, Dimitri Roditchev, Hervé Aubin, Guy Allan, Christophe Delerue, Christophe DavidAbstract:In the recent work of Vlaic et al. [Nat. Commun. 8, 14549 (2017)], it has been shown that Pb nanocrystals grown on the electron accumulation layer at the (110) surface of InAs are in the regime of Coulomb blockade. This enabled a scanning tunneling spectroscopy study of the superconducting parity effect across the Anderson limit. The nature of the tunnel barrier between the nanocrystals and the substrate has been attributed to a Quantum constriction of the electronic wave function at the interface due to the large Fermi wavelength of the electron accumulation layer in InAs. In this paper, we detail and review the arguments leading to this conclusion. Furthermore, we show that, thanks to this highly clean tunnel barrier, this system is remarkably suited for the study of discrete electronic levels induced by Quantum Confinement effects in the Pb nanocrystals. We identified three distinct regimes of Quantum Confinement. For the largest nanocrystals, Quantum Confinement effects appear through the formation of Quantum well states regularly organized in energy and in space. For the smallest nanocrystals, only atomiclike electronic levels separated by a large energy scale are observed. Finally, in the intermediate size regime, discrete electronic levels associated to electronic wave functions with a random spatial structure are observed, as expected from random matrix theory.
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Quantum Confinement in the Si-III (BC-8) phase of porous silicon
Applied Physics Letters, 1997Co-Authors: Guy Allan, Christophe Delerue, Michel LannooAbstract:Porous silicon was recently shown to give rise to the same semimetallic Si-III (BC-8) phase as silicon upon application and release of high pressure. This phase is known to have a direct gap and we examine the effect of Quantum Confinement on its electronic structure. This is performed by combining empirical tight binding and ab initio local density calculations. The blue shift is found to be similar to what is obtained for nanocrystallites with the diamond structure and the radiative recombination rate is much larger. Comparison with experiment shows that the observed luminescence is not consistent with the Quantum Confinement hypothesis.
