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1

Surface Plasmon Frequency Spectrum in a System of Two Spherical Dielectric Coated Metallic Nanoparticles

100%

Makaryan T., Melikyan A., Minassian H.

Acta Physica Polonica A

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2007

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vol. 112

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issue 5

1025-1029

EN

Semi-analytical method of surface plasmon frequency calculation for the system of two almost touching coupled dielectric coated metallic nanospheres is presented. The method allows transforming the problem to numerical solution of two simple algebraic equations for arbitrary values of parameters - particle radius, distance between sphere centers, dielectric permittivity of the matrix, dielectrics and metals. It is especially easy to get the obvious graphical solution. The surface plasmon frequencies of longitudinal and transversal oscillations of the system are calculated and good agreement with the experimental results is achieved.

2

Simulating the Electron Transmission with Different Defective Carbon Nanotubes

100%

Nizam R., Rizvi S., Azam A.

Acta Physica Polonica A

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2012

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vol. 122

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issue 1

190-196

EN

2. The transmissions of forty-eight carbon nanotube geometries to form twenty-four intramolecular junctions between every two carbon nanotubes and two simple carbon nanotubes are also taken for investigating numerically. These forty-eight carbon nanotubes form three different kinds of intramolecular junctions, which mean that each sixteen carbon nanotubes are identical to either sixteen carbon nanotubes in all respect, except three different intramolecular junctions in between them. The three intramolecular junctions, named as circumferential defective carbon nanotubes, grouped defective carbon nanotubes and distributed defective carbon nanotubes. The nature of electronic states at the interfaces and in the semiconductor section is analyzed with the help of tight-binding method. These quantum transmissions have been compared among the different defective carbon nanotubes and have been correlated with the pentagon and heptagon that formed in the intramolecular junction. It has been simulated that each pair of semiconductor-semiconductor carbon nanotubes, semiconductor-metallic carbon nanotubes and metallic-metallic carbon nanotubes transmission affect on the presence of junctions pentagons-heptagons. The least deviations transmission is observed in the circumferential defective carbon nanotubes rather than in other two and the maximum deviations are seen in the grouped defective carbon nanotubes irrespective of the joining of the carbon nanotube interface.

3

Hole Subband Mixing and Polarization of Luminescence from Quantum Dashes: A Simple Model

63%

Kaczmarkiewicz P., Musiał A., Sęk G., Podemski P., Machnikowski P., Misiewicz J.

Acta Physica Polonica A

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2011

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vol. 119

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issue 5

633-636

EN

In this paper, we address the problem of luminescence polarization in the case of nanostructures characterized by an in-plane shape asymmetry. We develop a simple semi-qualitative model revealing the mechanism that accounts for the selective polarization properties of such structures. It shows that they are not a straightforward consequence of the geometry but are related to it via valence subband mixing. Our model allows us to predict the degree of polarization dependence on the in-plane dimensions of investigated structures assuming a predominantly heavy hole character of the valence band states, simplifying the shape of confining potential and neglecting the influence of the out-of-plane dimension. The energy dependence modeling reveals the importance of different excited states in subsequent spectral ranges leading to non-monotonic character of the degree of polarization. The modeling results show good agreement with the experimental data for an ensemble of InAs/InP quantum dashes for a set of realistic parameters with the heavy-light hole states separation being the only adjustable one. All characteristic features are reproduced in the framework of the proposed model and their origin can be well explained and understood. We also make some further predictions about the influence of both the internal characteristics of the nanostructures (e.g. height) and the external conditions (excitation power, temperature) on the overall degree of polarization.

4

Correlations in Hexagonal Lattice Systems - Application to Carbon Nanotubes

63%

Czajka K., Maśka M.

Acta Physica Polonica A

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2004

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vol. 106

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issue 5

703-707

EN

We present exact diagonalization studies of two-dimensional electron gas on hexagonal lattice. Using Lanczös method we analyze the influence of the Coulomb correlations on the density of states and spectral functions. Choosing appropriate boundary conditions we simulate the geometry of a single wall carbon nanotube. In particular, integration over the boundary condition in one direction and summation in the other one allows us to perform cluster calculations for a tube-like system with a finite diameter and infinite length.

5

Electron Transmission through Graphene Bilayer Flakes

63%

Chico L., González J., Santos H., Pacheco M., Brey L.

Acta Physica Polonica A

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2012

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vol. 122

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issue 2

299-303

EN

We investigate the electronic transport properties of a bilayer graphene flake contacted by two monolayer nanoribbons. This finite-size bilayer flake can be built by overlapping two semi-infinite ribbons. We study and analyze the electronic behavior of this structure by means of a tight-binding method and a continuum Dirac model. We have found that the conductance oscillates markedly between zero and the maximum value of the conductance, allowing for the design of electromechanical switches.

6

Transport and Capacitance Spectroscopy of Quantum Dots

63%

Adamowski J., Bednarek S., Szafran B.

Acta Physica Polonica A

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2001

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vol. 100

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issue 2

145-163

EN

A review of recent theoretical studies on a single-electron tunneling in quantum dots is presented. This effect underlies the transport spectroscopy performed on the vertical gated quantum dots and the capacitance spectroscopy on the self-assembled quantum dots. The conditions of the single-electron tunneling are formulated in terms of electrochemical potentials of the electrons in the leads and in the quantum dot. The electrochemical potentials for the electrons confined in the quantum dots can be calculated by solving the many-electron Schrödinger equation. The results obtained by the Hartree-Fock method are presented. For the vertical gated quantum dot, the realistic confinement potential is obtained from the Poisson equation. The application of the self-consistent procedure to the solution of the Poisson-Schrödinger problem is discussed. The calculated positions of the current peaks at zero bias and boundaries of the Coulomb diamonds for non-zero bias are in good agreement with experiment. The influence of an external magnetic field on the single-electron tunneling is also discussed. The spin-orbital configurations of the electrons confined in the quantum dots change with the magnetic field, which leads to features observed in the current-voltage and capacitance-voltage characteristics.

7

Influence of Valence Band Modifications on Hydrogen Absorption in Zr-Pd Alloy Thin Films

63%

Jabłoński B., Pacanowski S., Werwiński M., Marczyńska A., Dawczak-Dębicki H., Szajek A., Smardz L.

Acta Physica Polonica A

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2018

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vol. 133

|

issue 3

620-623

EN

We study the valence band modifications of in-situ prepared nano- and polycrystalline Pd-Zr alloy thin films using X-ray photoelectron spectroscopy. Results were compared with valence bands calculated by ab initio methods. Furthermore, hydrogen absorption and desorption kinetics under pressure of about 570 mbar were studied in Pd covered nanocrystalline ZrPd₂ alloy thin film. Results showed that modifications of the valence band of the nanocrystalline alloy thin film could significantly influence on hydrogen absorption and desorption process.

8

Electronic Shells of Dirac Fermions in Graphene Quantum Rings in a Magnetic Field

63%

Potasz P., Güçlü A., Hawrylak P.

Acta Physica Polonica A

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2009

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vol. 116

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issue 5

832-834

EN

We present results of tight binding calculations demonstrating existence of degenerate electronic shells of Dirac fermions in narrow, charge neutral graphene quantum rings. We predict removal of degeneracy with finite magnetic field. We show, using a combination of tight binding and configuration interaction methods, that by filling a graphene ring with additional electrons this carbon based structure with half-filled shell acquires a finite magnetic moment.

9

Band Structure and Quantum Conductance of Metallic Carbon Nanotube Superlattices

63%

Jaskólski W., Stachów A., Chico L.

Acta Physica Polonica A

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2005

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vol. 108

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issue 4

697-704

EN

The electronic structure and quantum conductance of rotationally invariant (6,6)/(12,0) and rotationally non-invariant (5,5)/(8,2) superlattices made of metallic carbon nanotubes are investigated. It is shown that, except in the limit of very large periods, the quantum conductance of such superlattices does not critically depend on their rotational invariance, although it does in case of quantum dots and single junctions made of these nanotubes.

10

XPS Valence Band Studies of LaNi_{5-x}Mₓ (M = Al, Co; x = 0, ,1) Alloy Thin Films

63%

Skoryna J., Marczyńska A., Pacanowski S., Szajek A., Smardz L.

Acta Physica Polonica A

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2015

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vol. 127

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issue 2

430-432

EN

LaNi_{5-x}Mₓ (M = Al, Co) alloy thin films were prepared onto oxidised Si(100) substrates in the temperature range of 285-700 K using UHV magnetron co-sputtering. The surface chemical composition and valence bands of all the alloy thin films were measured in situ, immediately after deposition, transferring the samples to an UHV analysis chamber equipped with X-ray photoelectron spectroscopy. Results showed that the shape of the valence bands measured for the polycrystalline samples is practically the same compared to those obtained theoretically from ab initio band structure calculations. On the other hand, the X-ray photoelectron spectroscopy valence bands of the nanocrystalline thin films (especially LaNi₄Co) are considerably broader compared to those measured for the polycrystalline samples. This is probably due to a strong deformation of the nanocrystals. Therefore, the different microstructure observed in polycrystalline and nanocrystalline alloy thin films leads to significant modifications of their electronic structure.

11

Electronic Properties of In Situ Prepared Nanocrystalline Fe-Ni-Ti Alloy Thin Films

63%

Pacanowski S., Skoryna J., Marczyńska A., Skoryna D., Smardz L.

Acta Physica Polonica A

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2015

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vol. 127

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issue 2

436-438

EN

In this contribution we study experimentally the electronic properties of nanocrystalline Fe-Ni-Ti alloy thin films using X-ray photoelectron spectroscopy. The structure of the samples has been studied by X-ray diffraction. Their bulk chemical compositions were measured using X-ray fluorescence method. The surface chemical composition and the cleanness of all samples were checked in situ, immediately after deposition, transferring the samples to an UHV analysis chamber equipped with X-ray photoelectron spectroscopy. X-ray diffraction studies revealed the formation of nanocrystalline Fe-Ni-Ti alloy thin films at a substrate temperature of about 293 K. In situ X-ray photoelectron spectroscopy studies showed that the valence bands of nanocrystalline samples are broader compared to those measured for the polycrystalline bulk alloys. Such modifications of the valence bands of the nanocrystalline alloy thin films could influence on their hydrogenation properties.

12

Collective Phenomena in Multiwall Carbon Nanotubes

63%

Margańska M., Szopa M., Zipper E.

Acta Physica Polonica A

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2004

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vol. 106

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issue 5

609-616

EN

Collective phenomena due to persistent currents in carbon multiwall nanotubes are studied. The formula for persistent currents minimising free energy and conditions for the stability of persistent currents in multiwall nanotubes in magnetic field are derived. Numerical calculations performed show the possibility of obtaining spontaneous currents in two optimal configurations: undoped armchair-only multiwall nanotubes up to 0.01 K, and zig-zag-chiral-chiral-zig-zag multiwall nanotubes doped to -3.033 eV up to about 1 K. The latter configuration may exhibit also the diamagnetic expulsion of magnetic field, which according to our calculations can reach 20% of the external flux.

13

Friedel Oscillations in Carbon Nanotube Quantum Dots and Superlattices

63%

Chico L., Santos H., Ayuela A., Pelc M., Jaskólski W.

Acta Physica Polonica A

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2008

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vol. 114

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issue 5

1085-1091

EN

Interface states of all-metallic carbon nanotube quantum dots and superlattices are studied within a tight-binding model. We focus on achiral systems made by connecting armchair (n,n) and zigzag (2n,0) tubes with a full ring of n pentagon-heptagon topological defects. We show that the coupling between interface states, which arise from the topological defects, reflects the existence of the Friedel oscillations in the (n,n) tube, with an unusually large decay exponent. We expect this interaction to be important for the understanding of other physical properties, such as selective dot growth, magnetic interaction through carbon tubes or optical spectroscopy of interface states.

14

Photoluminescence Dynamics of GaN/Si Nanowires

51%

Korona K., Zytkiewicz Z., Perkowska P., Borysiuk J., Binder J., Sobanska M., Klosek K.

Acta Physica Polonica A

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2012

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vol. 122

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issue 6

1001-1003

EN

In this work we present analysis of carriers dynamics in samples of GaN nanowires grown on silicon. The samples exhibit bright luminescence of bulk donor-bound excitons at 3.472 eV, surface defect-bound excitons at 3.450 eV (SDX) and a broad (0.05 eV) band centered at 3.47 eV caused probably by single free exciton and bi-exciton recombination. The SDX emission has long lifetime τ = 0.6 ns at 4 K and can be observed up to 50 K. At higher temperatures luminescence is dominated by free excitons. The broad excitonic band is best visible under high excitation, and reveals fast, non-exponential dynamics. We present mathematical model assuming exciton-exciton interaction leading to the Auger processes. The model includes n^2 (Langevin) term and describes well the non-exponential dynamics of the excitonic band.

15

Multiband Electronic Structure of Magnetic Quantum Dots: Numerical Studies

51%

Rederth D., Oszwałdowski R., Petukhov A., Pientka J.

Acta Physica Polonica A

|

2018

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vol. 133

|

issue 3

343-349

EN

Semiconductor quantum dots (QDs) doped with magnetic impurities have been a focus of continuous research for a couple of decades. A significant effort has been devoted to studies of magnetic polarons (MP) in these nanostructures. These collective states arise through exchange interaction between a carrier confined in a QD and localized spins of the magnetic impurities (typically: Mn). Our theoretical description of various MP properties in self-assembled QDs is discussed. We present a self-consistent, temperature-dependent approach to MPs formed by a valence band hole. The Luttinger-Kohn k· p Hamiltonian is used to account for the important effects of spin-orbit interaction.

16

Energy and Optical Absorption Spectra of Multiply Charged Anisotropic Quantum Boxes

51%

Trojnar A., Małachowski T., Wójs A.

Acta Physica Polonica A

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2007

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vol. 112

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issue 2

173-176

EN

Using a simple model of a two-dimensional rectangular quantum box we study the effects of size and anisotropy on the energy and photoluminescence spectra of neutral and charged quantum dots. The competition of symmetries and energy/length scales of the free exciton or trion and of the confining potential is analyzed. The numerical calculations consisted of the diagonalization of the few-electron-hole Hamiltonian matrices in the full configuration-interaction basis, with the simultaneous resolution of the conserved orbital and spin quantum numbers.

17

Electronic Band Structure of Coiled Carbon Nanotubes

51%

Milošević I., Damnjanović M.

Acta Physica Polonica A

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2011

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vol. 120

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issue 2

221-223

EN

More than fifteen years have passed since the first report of experimental evidence of regularly coiled carbon nanotubes, but, the structure, formation mechanism and theoretical aspects of these nanotubes still remain unresolved. We propose model of hexagonal, helically coiled single wall carbon nanotubes, determine their line group symmetry and calculate electronic band structure of the relaxed configurations by means of fully symmetry adopted density functional tight binding method implemented into the POLSym code. Electrical properties of the straight and coiled carbon nanotubes of different chiralities are compared and analyzed.

18

Size Effects in Radiospectroscopy Spectra of Ferroelectric Nanopowders

51%

Glinchuk M., Kondakova I., Laguta V., Slipenyuk A., Bykov I., Ragulya A., Klimenko V.

Acta Physica Polonica A

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2005

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vol. 108

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issue 1

47-60

EN

The theoretical and experimental investigation of ferroelectric nanopowders is performed. The manifestation in radiospectroscopy spectra of size driven ferroelectric-paraelectric phase transition at some critical particle average size R = R_c was the main goal of the consideration. In theoretical part the size effect for the materials with ferroelectric tetragonal phase at room temperature and cubic paraelectric phase was considered allowing for the spontaneous polarization inhomogeneity inside a particle and distribution of particle sizes. In ESR the transformation of the spectra from tetragonal symmetry to cubic symmetry lines with decrease in nanoparticle sizes was calculated. The method of R_c value extraction from the ratio of the different symmetry lines intensities in the absorption spectra was proposed. Measurements of Fe^{3+} ESR spectra in nanopowder of BaTiO_3 were carried out at room temperature. The samples were prepared by rate-controlled method with different particle sizes, which depend on annealing temperature. The decrease in intensity of tetragonal symmetry ESR lines of Fe^{3+} and appearance of cubic symmetry line with asymmetry of the shoulders was observed with the average sizes decrease with complete disappearance of tetragonal spectrum at R ≤ 40 nm. The comparison of the theory with experiment was carried out. The theory fits experimental data pretty good. The value of critical size R_c ≈ 40 nm was extracted from ESR data. The asymmetry and broadening of right hand side shoulder of ESR cubic symmetry line was shown to be related to contribution of paramagnetic centers in the vicinity of the particles surface with lower than cubic symmetry. The deconvolution of the cubic line allowed to show that this region size is about 3 nm.

19

Ab Initio Analysis of a Quantum Dot Induced by a Local External Potential in a Semiconducting Carbon Nanotube

51%

Kostyrko T., Krompiewski S.

Acta Physica Polonica A

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2009

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vol. 115

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issue 1

387-389

EN

Using the density functional theory we study the influence of external charge probes on the electronic structure of semiconducting carbon nanotubes in the vicinity of the Fermi level. We show that the spatially limited potential due to the probe can create localized electronic states in the energy gap and at the edges of the conductance band. By filling these localized states with additional electrons one obtains a quantum dot, which can be tuned by modifying the properties of the external charge probe. We analyze dependence of the electronic structure of the dot on the spatial extension of the potential as well as on the nanotube radius.

20

Quantized Absorption Strength of Multi-Exciton Quantum Dots

51%

Wójcik K., Grodecka A., Wójs A.

Acta Physica Polonica A

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2006

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vol. 110

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issue 3

423-428

EN

Energy and absorption/recombination spectra of up to two electron-hole pairs confined in a spherical quantum dot are studied numerically as a function of dot radius (i.e., confinement volume). The transition between fermionic and bosonic behavior of the confined excitons is identified in coincidence with enhancement of low-energy absorption strength.

Refine search results

Surface Plasmon Frequency Spectrum in a System of Two Spherical Dielectric Coated Metallic Nanoparticles

Simulating the Electron Transmission with Different Defective Carbon Nanotubes

Hole Subband Mixing and Polarization of Luminescence from Quantum Dashes: A Simple Model

Correlations in Hexagonal Lattice Systems - Application to Carbon Nanotubes

Electron Transmission through Graphene Bilayer Flakes

Transport and Capacitance Spectroscopy of Quantum Dots

Influence of Valence Band Modifications on Hydrogen Absorption in Zr-Pd Alloy Thin Films

Electronic Shells of Dirac Fermions in Graphene Quantum Rings in a Magnetic Field

Band Structure and Quantum Conductance of Metallic Carbon Nanotube Superlattices

XPS Valence Band Studies of LaNi_{5-x}Mₓ (M = Al, Co; x = 0, ,1) Alloy Thin Films

Electronic Properties of In Situ Prepared Nanocrystalline Fe-Ni-Ti Alloy Thin Films

Collective Phenomena in Multiwall Carbon Nanotubes

Friedel Oscillations in Carbon Nanotube Quantum Dots and Superlattices

Photoluminescence Dynamics of GaN/Si Nanowires

Multiband Electronic Structure of Magnetic Quantum Dots: Numerical Studies

Energy and Optical Absorption Spectra of Multiply Charged Anisotropic Quantum Boxes

Electronic Band Structure of Coiled Carbon Nanotubes

Size Effects in Radiospectroscopy Spectra of Ferroelectric Nanopowders

Ab Initio Analysis of a Quantum Dot Induced by a Local External Potential in a Semiconducting Carbon Nanotube

Quantized Absorption Strength of Multi-Exciton Quantum Dots