Breakdown Of Selection Rules Research Articles

Tailoring the photophysical properties of carbon nanotubes by photonic nanostructures

Single-walled carbon nanotubes (SWCNTs) are nearly ideal one-dimensional systems with potential applications in a wide range of fields. The rich physics of SWCNTs arise from the excitonic nature of their photophysical properties. This review is focused on the results of novel research activities that explore how the photophysical properties of SWCNTs can be altered via their integration with photonic nanostructures including plasmonic structures and photonic microcavities that have resulted in phenomena such as photocurrent enhancement, selection rule breakdown and photoluminescence (PL) modification.

28aDA-2 局在プラズモン励起における単層カーボンナノチューブの電子遷移選択則の破れ : 理論(プラズモン・近接場分光,非線形光学,超イオン導電体,領域5(光物性))

28aDA-2 局在プラズモン励起における単層カーボンナノチューブの電子遷移選択則の破れ : 理論(プラズモン・近接場分光,非線形光学,超イオン導電体,領域5(光物性))

Structural phenomena of metamict titanite: a synchrotron, X-ray diffraction and vibrational spectroscopic study

Titanite, CaTiSiO5, occurs in nature in crystalline and metamict modification. Its structure consists of corner-linked TiO6 octahedra, SiO4 tetrahedra and sevenfold coordinated Ca. Metamictization occurs when a mineral contains impurities like U and Th and is exposed to radioactive irradiation. Recoil processes due to alpha radiation change over geological time scales the structure to a state with persisting short-range order but violated long-range order. Raman and infrared spectra and X-ray diffraction data of metamict as well as crystalline and titanite glass reveal local structural phenomena. Raman spectra of metamict titanite differ from spectra of well-crystalline titanite, indicating the breakdown of selection rules. Raman scattering reveals that anisotropy is preserved upon metamictization and that the structural state of highly metamict titanite should not be considered as quasi-amorphous. The metamict state partially recovers its disorder via heat treatment. Annealing-induced shrinking of unit cell volume is related to stiffening and improved local symmetry of SiO4 tetrahedra.

Exact diagonalization studies of inelastic light scattering in self-assembled quantum dots

We report exact diagonalization studies of inelastic light scattering in few-electron quantum dots under the strong confinement regime characteristic of self-assembled dots. We apply the orthodox (second-order) theory for scattering due to electronic excitations, leaving for the future the consideration of higher-order effects in the formalism (phonons, for example), which seem relevant in the theoretical description of available experiments. Our numerical results stress the dominance of monopole peaks in Raman spectra and the breakdown of selection rules in open-shell dots. The dependence of these spectra on the number of electrons in the dot and the incident photon energy is explicitly shown. Qualitative comparisons are made with recent experimental results.

Interface formation of Mg with DiMePTCDI studied by Raman spectroscopy

Metal/organic interfaces play an important role in the performance of organic based devices. In this work the interface formation between Mg and N,N′-DiMethyl-3,4,9,10-Perylene Tetra Carboxylic DiImide (DiMePTCDI) films grown on sulphur-passivated GaAs (100) substrates is investigated in situ by Raman spectroscopy. The Raman spectra are taken in a backscattering geometry at room temperature under resonance conditions with the 488 nm (2.54 eV) Ar+ laser line. They reveal that when Mg is deposited onto a 15 nm DiMePTCDI layer the external phonon modes are preserved up to large metal coverages. Since these modes are a fingerprint of the molecular crystal, their preservation indicates a low diffusion of Mg into the DiMePTCDI layer. Concerning the internal molecular modes, the Mg deposition induces a breakdown of selection rules which is proposed to originate from a dynamical charge transfer between the DiMePTCDI molecules and the metal. Above 0.3 nm nominal thickness of Mg the line-shape of the molecular breathing mode at 221 cm–1 develops an asymmetric tail towards higher frequencies. A similar effect is observed for the bands that occur at 1291 cm–1 and 1606 cm–1 but the asymmetry appears at the low frequency side. This line-shape asymmetry is likely to be related to a Fano resonant coupling between the molecular vibrational modes and the electronic continuum of states of metallic clusters formed above 0.3 nm Mg coverage. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Raman monitoring of In and Ag growth on PTCDA and DiMe-PTCDI thin films

The formation of In and Ag interfaces with 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) and N, N′-dimethyl-3,4,9,10-perylene tetracarboxylic diimide (DiMe-PTCDI) was investigated by in situ Raman spectroscopy in order to determine the interaction between the metals and the organic molecules. A significant enhancement of internal vibrational modes is observed in all cases, clearly indicating the presence of surface enhanced Raman scattering. The molecules having direct contact with the metal are involved in a weak ground state dynamical charge transfer resulting in a breakdown of selection rules. However, there is no indication for the formation of new chemical bonds. In the case of In deposition on PTCDA, this contradicts previous models of covalent bond formation between In and O atoms in PTCDA. The enhancement factors of the Raman signals can be employed to extract information on indiffusion and morphology of the metals. Both metals exhibit rough morphologies of different degrees and depending on the organic substrate. In addition, In shows the strongest tendency of indiffusion when deposited on PTCDA. This is corroborated by the rapid disappearance of intermolecular, i.e. phonon-like modes in the frequency range below 120 cm −1.

Interaction between metals and organic semiconductors studied by Raman spectroscopy

Silver and indium were deposited onto molecular layers of two perylene derivatives, viz. 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) and N,N′-dimethylperylene 3,4,9,10-dicarboximide (DiMe–PTCDI). The interaction between the metals and the organic semiconductors was probed in situ by Raman spectroscopy. The molecular structure is found to be preserved when Ag or In are deposited onto PTCDA and DiMe–PTCDI layers. For In, this is in contrast to previous suggestions of strong reactivity with PTCDA and covalent bond formation between In and O atoms in PTCDA. However, the molecules having direct contact with the metal are involved in a ground state dynamical charge transfer with different strength for Ag and In, resulting in a breakdown of vibrational selection rules. A significant enhancement of Raman internal vibrational modes is observed both for Ag and In deposition as a result of metal-induced surface enhanced Raman scattering (SERS). The enhancement factors observed for the internal modes reflect a rough morphology of the metal films which is influenced by the morphology of the underlying organic film. Moreover, conclusions regarding the indiffusion of the two metals can be drawn from the comparison of the breakdown of the selection rules for the internal modes and the spectral evolution of the external molecular modes.

Double photoionization in the case of unequal energy sharing

The triply differential cross section (TDCS) for double photoionization of helium is calculated using a three-body Coulomb correlated final state wavefunction which treats the three Coulomb particles on an equal basis. Complementary to preceding publications by Maulbetsch and Briggs (1992, 1993) emphasis is given to the case of unequal sharing of the available excess energy. The breakdown of selection rules which apply in the equal energy sharing case leads to a greater variety of angular patterns. Excellent agreement is obtained with the first experimental results for unequal energy sharing.

Potential energy surface and vibrational analysis along the stretching vibrations of XeHXe+ ion

An analytical potential energy surface (PES) along the stretching coordinates of a linear XeHXe+ ion is presented. Ab initio calculations within the effective core potential approach are used as input for the PES. The present vibrational analysis indicates extensive mixing of the zeroth-order harmonic oscillator vibrational states, and a rather complete collapse of the normal mode picture already near the bottom of the potential well. At higher vibrational energies, and elongated Xe–Xe distances, development of a double minimum in the PES is observed. The simulated absorption spectrum consists of a strong vibrational progression near 1000–1700 cm−1, and is in qualitative agreement with the previous matrix isolation data. The intensity distribution of the vibrational progression is mostly due to the potential terms rather than nonlinear contributions in the Taylor series expansion of the electric dipole moment. Due to the highly anharmonic potential, and subsequent breakdown of selection rules, the emission spectrum is predicted to be particularly rich in the 850–1500 cm−1 spectral region. Several of the vibrational transitions possess transition dipoles exceeding 1 D.

Selection-rule breakdown in coherent resonant tunneling in a tilted magnetic field.

We report on a study of resonant tunneling in a magnetic field tilted with respect to the current direction on a double-barrier structure. A splitting of the resonant current peak into several satellites is observed and corresponds to tunneling with nonconservation of the Landau-level index. We propose a simple coherent-tunneling model that accounts very well for both positions and magnitudes of the observed features, and we show that these experiments clearly evidence new selection rules for tunneling in a tilted magnetic field.

Is there a Signature of the Chaoticity of the Asssociated Classical System in the Spectrum of a Quantum System?

AbstractThe cause of the appearance of chaos in classical dynamics is the disappearance of first integrals of the movement which restrict the motion of the configuration point in phase space. This enables the system to wander in increasing parts of the phase space. The direct consequence in quantum mechanics is the disappearance of quantum numbers and of the corresponding selection rules. We will discuss two consequences of this disappearance of selection rules.(1) Level repulsion enabled by breakdown of selection rules. While most papers deal with nearest neighbour spacing distribution, we will show that the most relevant consequence on the dynamical behavior is intermediate and long range correlations between level positions. We will display the correspondence between dynamical evolution in classical, semiclassical limit, and full quantum mechanical versions of a given system.(2) Periodic simplification of spectra due to periodic reestablishment of approximate quantum numbers and associated selection rules, and its counterpart in chaotic or regular parts of classical phase space, in the case of molecular Rydberg states.

Lattice Mode Study of La2CuO4-y Implanted with Sr

ABSTRACTDramatic implantation-induced changes in the Raman and infrared spectra of polycrystalline samples of La2CuO4-y are reported for implantation of Sr in the fluence range 0.5 to 1.5 × 1016/cm2. The Raman and ir-reflectance spectra of the Sr implanted material reveal disorder-induced lines corresponding to breakdown of selection rules and to non-zone-center phonon modes. Whereas the main features in the Raman spectra of the implanted sample are broad disorder-induced lines centered at ∼ 560 ± 5 cm−1, reststrahlen lineshapes are observed above ∼ 800 cm−1 in the ir-reflectance spectra. After thermal annealing (550°C), the multiphonon lines in the ir spectra diminish, and the disorder-induced lines in the Raman spectra split to form well-resolved, sharper lines at 530 and 580 cm−1, identified with maxima in the phonon density of states. The sensitivity and complementarity of Raman and infrared spectroscopy to implantation-induced disorder and subsequent partial recovery by thermal annealing suggest that these techniques can be used to characterize sensitively disorder in ion implanted La2CuO4-y high Tc, materials.

Measurement of Raman scattered intensities in media with natural or field‐induced optical activity

AbstractThe intensity of Raman scattered light has been calculated for gyrotropic media, i.e. for media with a natural optical activity or a gyrotropy induced by a magnetic field. It is shown that anomalies in the scattered intensity are in general due to interference effects between the two orthogonally polarized normal modes of electromagnetic radiation propagating in the anisotropic crystal either in the incident or in the scattered beam or in both. Only when the state of polarization of the incident and the scattered waves agrees with one of these normal modes are clear results obtained which are simply to interpret. Hence the intensity anomalies sometimes observed in these media find an interpretation in the frame of the generally accepted theory. No breakdown of selection rules will occur in such media.The calculated results are compared with experimental findings in α‐quartz and in ZnP2 and also in paramagnetic TmVO4 and in CeF3 in external magnetic fields.

A comparative study of (100) GaAs films grown by liquid-phase epitaxy, molecular-beam epitaxy and metal-organic chemical vapor deposition by Raman spectroscopy

We investigated (100) GaAs films grown by liquid-phase epitaxy, molecular-beam epitaxy and metal-organic chemical vapor deposition by Raman spectroscopy. The crystalline quality of the epitaxial films grown by the different techniques, as determined by the linewidth and intensity of the symmetry-allowed LO phonon lines, is found to be comparable. Symmetryforbidden TO phonon lines were observed in some undoped molecular-beam epitaxial films, and in heavily doped p-type (≳ 10 18 cm −3) samples. The possible causes for its presence in each case are discussed. The Raman spectrum obtained from an interfacial region between GaAs and Al 0.35 Ga 0.65 As films showed an enhancement of the LO phonon-plasmon coupled mode and the TO mode presumably due to reduced carrier depletion near the interface and breakdown of selection rules due to disorder, respectively. It is suggested that Raman spectroscopy can be used as a technique to characterize interfaces in a multilayer structure.

Resonant polaron coupling of the n = 1 Landau level and the 2p + donor state in GaAs

The n = 0 → > n = 1 Landau level and 1 s −2 p + impurity transitions in GaAs were investigated up to energies above the optical phonon energy ħΩ LO and d.c. magnetic fields up to 25 T. Pinning of both transitions to an energy slightly above and below ħΩ LO was observed. At an energy very close to ħΩ LO two additional impurity transitions are found. These features are attributed to the resonant polaron effect which leads to hybridization and dipole selection rule breakdown. Also the spin doublet splitting of both transitions were resolved showing a strong magnetic field dependence which can not be explained by nonparabolicity of the conduction band alone.

Study by Raman spectroscopy of order‐disorder phenomena occurring in some binary oxides with fluorite‐related structures

AbstractOrder‐disorder phenomena in binary oxides with fluorite‐related structures were studied by Raman spectroscopy.Raman spectra of disordered phases show broad bands, defects leading to selection rule breakdown. For well‐ordered structures, the scattering active modes observed are those allowed by crystal symmetry. Broadening of Raman peaks occurs when order defects are present: antiphase boundaries, distribution of different cations on equivalent crystallographic positions.

Lattice modes and charge density waves in 1T-TaS 2

The far-infrared reflectivity of 1T-TaS 2 was measured at 100, 295 and 390 K. At the two highest temperatures, the spectra were featureless. Overall reflectivity dropped abruptly in cooling through 350 K and through 190 K. These transitions are correlated to CDW formation. At 100 K five strong bands and at least two weak bands were observed. These are attributed to lattice vibration which can be excited optically as a result of the breakdown of selection rules due to the formation of a large superlattice by the onset of CDW.

Breakdown of selection rules in the Raman spectra of KDP

Raman spectra of A1 and B1 modes of KH2PO4 single crystal are studied experimentally by varying the orientation of the crystal axes relative to the incident and scattered light directions. It has been found that the scattering intensities depend on the k vector of the scattering phonons, thus invalidating the selection rules in the first order Raman scattering.

The dielectric and lattice vibrational spectrum of cuprous oxide

The i.r. reflection and Raman spectra of single crystal specimens of cuprous oxide have been studied between 20 and 900 cm−1 over a wide temperature range. The optical and dielectric parameters have been derived by Kramers-Krönig analysis and the effective dynamic charge calculated. The Raman spectrum is far more complex than a group theoretical analysis suggests and this is interpreted in terms of a selection rule breakdown in the crystal due to nonstoichiometry. Variable temperature and polarisation measurements have been made in order to characterise some of the structure in the spectrum. The implications of the results for the lattice dynamical calculations is discussed.

Raman scattering from Ca xZr 1− xO 2− x阳 x, a system with massive point defects

Raman spectra have been measured on a series of solid solutions in the system ZrO 2-CaO at compositions consisting of a two-phase mixture of monoclinic ZrO 2 and calcium-saturated cubic ZrO 2 and of single-phase fluorite structure Ca x Zr − x O 2− x 阳 x . It is shown that introduction of translational disorder through random substitution of Ca 2+ cations and anion vacancies leads to complete breakdown of selection rules and the production of a spectrum that essentially represents the frequency distribution of the density of states in agreement with theoretical predictions.