Properties Of Electronic States Research Articles

Effect of the δ-shaped quantum well at the one-dimensional lattice boundary on properties of Tamm-type surface electronic states

The Tamm-type surface electronic states at the boundary of the one-dimensional structure with periodically potential profile have been theoretically studied under the condition that the δ-shaped quantum well is at this boundary. The properties of surface electronic states in such a structure have been compared with Tamm electronic states in the absence of a quantum well at the lattice boundary and with electronic states localized near the δ-shaped potential well deep in the lattice. In particular, it has been shown that the existence of the δ-shaped potential well at the lattice boundary facilitates a significant increase in the degree of localization of Tamm-type surface electronic states and makes possible the appearance of these states at arbitrarily small heights of lattice potential barriers.

ChemInform Abstract: Electronic States and Transport Properties of Carbon Crystalline: Graphene, Nanotube, and Graphite

AbstractReview: 96 refs.

Control over topological insulator photocurrents with light polarization

Three-dimensional topological insulators represent a new quantum phase of matter with spin-polarized surface states that are protected from backscattering. The static electronic properties of these surface states have been comprehensively imaged by both photoemission and tunnelling spectroscopies. Theorists have proposed that topological surface states can also exhibit novel electronic responses to light, such as topological quantum phase transitions and spin-polarized electrical currents. However, the effects of optically driving a topological insulator out of equilibrium have remained largely unexplored experimentally, and no photocurrents have been measured. Here, we show that illuminating the topological insulator Bi(2)Se(3) with circularly polarized light generates a photocurrent that originates from topological helical Dirac fermions, and that reversing the helicity of the light reverses the direction of the photocurrent. We also observe a photocurrent that is controlled by the linear polarization of light and argue that it may also have a topological surface state origin. This approach may allow the probing of dynamic properties of topological insulators and lead to novel opto-spintronic devices.

Synthesis, Electronic States, and Electroluminescent Properties of Aluminum Complex Based on Mixed Ligands with 8-Hydroxyquinolinate and Acetylacetone

We report the synthesis, photophysical investigation, computational studies and electroluminescent(EL) properties of an organic electroluminescent material-Bis(8-hydroxyQuino line) acetylacetone aluminum (Alq2A). It is characterized by 1H NMR, IR and elemental analysis techniques. The absorption and fluorescence spectra of various Alq2A systems including solution in ethanol, powder and thin film on quartz (thickness of 50nm) have also been systematically evaluated. Analysis of the electronic structure of Alq2A calculated by quantum chemical calculations reveals a localization of orbital and the distribution of orbital energy. The results from EL experiments indicate that Alq2A has good electron transport properties as compared with tris(8-hydroxyquinolinato) aluminum (Alq3). Thus, Alq2A is considered to be a superior emitter and electron transporting material for display application compared with Alq3.

MRCI study of spectroscopic and molecular properties of X2Πg, a 4Πu, A2Πu, b 4 , D2Δg and B2 electronic states of ion

The potential energy curves (PECs) of six low-lying electronic states (X2Πg, a 4Πu, A2Πu, b 4 , D2Δg and B2 ) of ion were studied by the ab initio quantum chemical method. The calculations were carried out with the full valence complete active space self-consistent field (CASSCF) method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach in combination with large correlation-consistent basis sets. Effects on the PECs of the core–valence correlation and relativistic corrections are taken into account. The way to consider the relativistic correction is to use the second-order Douglas–Kroll Hamiltonian (DKH2) approximation. The core–valence correlation correction is carried out with the cc-pCVQZ basis set, and the relativistic correction is performed at the level of cc-pVQZ basis set. To obtain more reliable results, the PECs determined by the MRCI calculations are also corrected for size-extensivity errors by means of the Davidson modification (MRCI + Q). These PECs are extrapolated to the complete basis set (CBS) limit by the two-point total-energy extrapolation scheme. With these PECs, the spectroscopic parameters (Te , De , D 0, Re , ωe , ωexe , αe and Be ) are determined and compared with those reported in the literature. The conclusion can be reached that the effect on the spectroscopic parameters of the core–valence correlation correction is larger than that of the relativistic correction. With the PECs obtained by the MRCI + Q/CV+DK+56 calculations, the vibrational levels and inertial rotation constants of the first 26 vibrational states are determined for these electronic states of non-rotating ion. Comparison with the experimental data shows that the present spectroscopic parameters and molecular constants are accurate.

MRCI study on spectroscopic and molecular properties of several low-lying electronic states of the CN radical

The potential energy curves (PECs) of eight low-lying electronic states ( X 2Σ +, A 2Π, B 2Σ +, a 4Σ +, D 2Π, E 2Σ +, 1 2Σ − and F 2Δ) of the CN radical have been studied using the ab initio quantum chemical method. The calculations have been performed using the complete active space self-consistent field (CASSCF) method followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with the correlation-consistent basis sets of Dunning and co-workers. The effects on the PECs by the core–valence correlation and relativistic corrections are taken into account. The way to consider the relativistic correction is to use the second-order Douglas–Kroll Hamiltonian approximation. The core–valence correlation correction calculations are performed with the cc-pCVQZ basis set. The relativistic correction is carried out at the level of cc-pV5Z basis set. In order to obtain more reliable results, the PECs determined by the MRCI calculations are also corrected for size-extensivity errors by means of the Davidson modification (MRCI+ Q). The PECs are extrapolated to the complete basis set (CBS) limit by the total-energy extrapolation scheme. With these PECs, the spectroscopic parameters ( T e , R e , ω e , ω e x e , ω e у e , B e , α e and γ e ) are determined and compared with those reported in the literature. Finally, with the PECs obtained by the MRCI+ Q/CV+DK+ Q5 calculations, the complete vibrational states are computed for the eight electronic states by solving the ro-vibrational Schrödinger equation for the non-rotating radical, and the vibrational levels and inertial rotation and centrifugal distortion constants of the first 11 vibrational states are reported, which agree favorably with the available experimental data. The spectroscopic parameters of 1 2Σ − and F 2Δ electronic states obtained by the MRCI+ Q/CV+DK+ Q5 calculations should be good predictions for future laboratory experiments.

PGO models in the envelope function and effective mass approximations

A recipe to design quantum devices that exhibit the theoretical pseudo-Gaussian oscillator electronic states properties is given. The algorithm is described en detail and is illustrated by the computation of a MnxCd1-xTe ternary alloy pseudo-Gaussian heterostructure. The numerical procedure reaches beyond of pseudo-Gaussian models and can be used for designing epitaxial growth devices with desired electronic states structure. The calculations are carried out in the envelope function and effective mass approximations.

Effects on spectroscopic properties for several low-lying electronic states of CS molecule by core–valence correlation and relativistic corrections

The PECs of a 3 Π, a ′ 3 Σ + , d 3 Δ, e 3 Σ − and A 1 Π of CS molecule have been studied using the CASSCF method followed by the MRCI approach with large correlation-consistent basis sets of Dunning and co-workers. Effects on the PECs by the core–valence correlation and relativistic corrections have been taken into account at the level of cc-pV5Z basis set. The way to consider the relativistic corrections is to use the second-order Douglas–Kroll Hamiltonian approximation. Using the CCSD(T), MRCI and MRCI with the Davidson modification, the PECs of electronic states involved are extrapolated to the CBS limit. With these PECs, the spectroscopic parameters and molecular constants of the electronic states involved are determined, which are in excellent agreement with the experimental data. Comparison with the measurements shows that the two-point total-energy extrapolation scheme can obviously improve the quality of spectroscopic parameters and molecular constants. ► Effect on the PECs by the core–valence correlation and relativistic corrections is considered. ► The PECs obtained by the CCSD(T), MRCI and MRCI + Q are extrapolated to the CBS limit. ► The energy extrapolation scheme obviously improves the quality of spectroscopic parameters. ► The spectroscopic parameters and molecular constants obtained achieve much high accuracy. The potential energy curves (PECs) of six low-lying electronic states (X 1 Σ + , a 3 Π, a ′ 3 Σ + , d 3 Δ, e 3 Σ − and A 1 Π) of CS molecule have been investigated using the full valence complete active space self-consistent field (CASSCF) method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach with large correlation-consistent basis sets. Effects on the PECs by the core–valence correlation and relativistic corrections have been taken into account. And the two corrections are performed at the level of cc-pV5Z basis set. The way to consider the relativistic corrections is to use the second-order Douglas–Kroll Hamiltonian approximation. Using the CCSD(T), MRCI and MRCI with the Davidson modification (MRCI + Q), the PECs of electronic states involved are extrapolated to the complete basis set (CBS) limit. With the PECs, the spectroscopic parameters ( T e , R e , ω e , ω e x e , ω e y e , α e , β e , γ e and B e ) of the six low-lying electronic states are determined. These parameters are in excellent agreement with the experimental data. The complete vibrational states are computed for the six low-lying electronic states when the rotational quantum number J equals zero, and the inertial rotation constants of the first 23 vibrational states are reported, which agree favorably with the RKR data. Comparison with the measurements shows that the two-point total-energy extrapolation scheme can obviously improve the quality of spectroscopic parameters and molecular constants.

Anomalous localization in the aperiodic Kronig–Penney model

We analyse the anomalous properties of specific electronic states in the Kronig–Penney model with weak compositional and structural disorder. Using the Hamiltonian map approach, we show that the localization length of the electronic states exhibits a resonant effect close to the band centre and anomalous scaling at the band edges. These anomalies are akin to the corresponding ones found in the Anderson model with diagonal disorder. We also discuss how specific cross-correlations between compositional and structural disorder can generate an anomalously localized state near the middle of the energy band. The tails of this state decay with the same stretched-exponential law which characterizes the band-centre state in the Anderson model with purely off-diagonal disorder.

Electronic Structure of Heme-Nitrosyls and Its Significance for Nitric Oxide Reactivity, Sensing, Transport, and Toxicity in Biological Systems

This review summarizes recent developments in the investigation of the electronic structures, spectroscopic properties, and reactivities of ferrous and ferric heme-nitrosyls and how this relates to important biological processes. Ferrous heme-nitrosyls show interesting variations in electronic structure as a function of the different types of proximal ligands, as is evident from electron paramagnetic resonance, magnetic circular dichroism, and vibrational spectroscopy. In particular, coordination of imidazoles like histidine (His) increases the radical character on NO and, in this way, could help activate the bound NO for catalysis. Vice versa, the bound NO ligand imposes a strong sigma trans effect on the proximal His, which, in the case of soluble guanylate cyclase (sGC), the biological NO sensor protein, induces breaking of the Fe(II)-His bond and activates the protein. The possibility of sGC activation by HNO is also discussed. Finally, the properties of ferrous heme-nitrosyls with proximal cysteinate (Cys) coordination are evaluated. It has been known for some time that ferric heme-nitrosyls are intrinsically more labile than their ferrous counterparts, but the underlying reasons for this observation have not been clarified. New results show that this property relates to the presence of a low-lying excited state that is dissociative with respect to the Fe(III)-NO bond. On the other hand, the ground state of these complexes is best described as Fe(II)-NO(+), which shows a very strong Fe-NO bond, as is evident from vibrational spectroscopy. NO, therefore, is a weak ligand to ferric heme, which, at the same time, forms a strong Fe-NO bond. This is possible because the thermodynamic weakness and spectroscopic strength of the Fe-NO bond relate to the properties of different electronic states. Thiolate coordination to ferric hemes leads to a weakening of both the Fe-NO and N-O bonds as a function of the thiolate donor strength. This observation can be explained by a sigma backbond into the sigma* orbital of the Fe-N-O unit that is mediated by the thiolate sigma-donor orbital via orbital mixing. This is a new interaction in heme-nitrosyl that has not been observed before. This also induces a bending of the Fe-N-O subunit in these cases. New spectroscopic data on a corresponding model complex are included in this paper. Finally, the mechanism of NO reduction by cytochrome P450nor is elucidated based on recent density functional theory results.

Controlling Electronic States and Transport Properties at the Level of Single Molecules

Since molecular electronics has been rapidly growing as a promising alternative to conventional electronics towards the ultimate miniaturization of electronic devices through the bottom-up strategy, it has become a long-term desire to understand and control the transport properties at the level of single molecules. In this Research News article it is shown that one may modify the electronic states of single molecules and thus control their transport properties through designing and fabrication of functional molecules or manipulating molecules with scanning tunneling microscopy. The rectifying effect of single molecules can be realized by designing a donor-barrier-acceptor architecture of Pyridine-sigma-C(60) molecules to achieve the Aviram-Ratner rectifier and by modifying electronic states through azafullerene C(59)N molecules. The effect of the negative differential resistances can be realized by appropriately matching the molecular orbital symmetries between a cobalt phthalocyanine (CoPc) molecule and a Ni electrode. The electronic states and transport properties of single molecules, such as CoPc and melamine molecules, can be altered through manipulation or modifying molecular structures, leading to functionalized molecular devices.

Localization properties of electronic states of one-dimensional Galois sequences

Galois sequences are aperiodic ordered structures, which have wide applications in many fields. In this paper, we study the electronic properties of the tight-binding model on Galois sequences. The energy spectra, wave functions and localization quantities are calculated. The results reveal that this model exhibits the Anderson localization feature.

Some Effective Tight-Binding Models for Electrons in DNA Conduction: A Review

Quantum transport for DNA conduction has been widely studied with interest in application as a candidate in making nanowires as well as interest in the scientific mechanism. In this paper, we review recent works concerning the electronic states and the conduction/transfer in DNA polymers. We have mainly investigated the energy-band structure and the correlation effects of localization property in the two- and three-chain systems (ladder model) with long-range correlation as a simple model for electronic property in a double strand of DNA by using the tight-bindingmodel. In addition, we investigated the localization properties of electronic states in several actual DNA sequences such as bacteriophages of Escherichia coli, human-chromosome 22, compared with those of the artificial disordered sequences with correlation. The charge-transfer properties for poly(dA)-poly(dT) and poly(dG)-poly(dC) DNA polymers are also presented in terms of localization lengths within the frameworks of the polaron models due to the coupling between the charge carriers and the lattice vibrations of the double strand of DNA.

Theoretical study of electronic structure and excited states properties of two dyes for dye-sensitized solar cells

Two conjugated organic dyes comprising the benzo[b]furan moieties as the electron donor and cyanoacetic acid moieties as the electron acceptor/anchoring groups have been investigated using a quantum chemical method. The molecular equilibrium geometries and ground state character were studied using density functional theory. Absorption spectra were obtained using time-dependent density functional theory and semiempirical ZINDO. The nature of absorption spectra was further studied using 2D and 3D real-space analysis; here, 2D real-space analysis showed electron–hole coherence, and 3D real-space analysis showed intramolecular charge transfer during photo-excitation. As important parameters, excited state oxidation potential and driving force energy were obtained to reveal the relationship between molecular structure and performance of two compounds.

Extension of Yafet's theory of spin relaxation to ferromagnets

By making use of Kramer's degeneracy of the electronic states in a nonmagnetic material, Yafet has derived an expression for the spin relaxation time T 1 due to scattering of electrons at phonons which involves the properties of electronic and phononic states and the matrix elements for the scattering. It is shown that an analogous expression for T 1 can be derived for ferromagnets (where Kramer's degeneracy does not hold) when taking into account the conservation of the total number of electrons. This expression can be used as a starting point for the ab initio calculation of T 1 , and this quantity is required for an interpretation of the ultrafast demagnetization of ferromagnets after excitation with a femtosecond laser pulse.

Nonclassical properties of electronic states of aperiodic chains in a homogeneous electric field

The electronic energy levels of one-dimensional aperiodic systems driven by a homogeneous electric field are studied by means of a phase space description based on the Wigner distribution function. The formulation provides physical insight into the quantum nature of the electronic states for the aperiodic systems generated by the Fibonacci and Thue-Morse sequences. The nonclassical parameter for electronic states is studied as a function of the magnitude of homogeneous electric field to achieve the main result of this work which is to prove that the nonclassical properties of the electronic states in the aperiodic systems determine the transition probability between electronic states in the region of anticrossings. The localisation properties of electronic states and the uncertainty product of momentum and position variables are also calculated as functions of the electric field.

Analysis of electronic parameters and interface states of boron dispersed triethanolamine/p-Si structure by AFM, I– V, C– V– f and G/ ω– V– f techniques

The electronic parameters and interface state properties of boron dispersed triethanolamine/p-Si structure have been investigated by atomic force microscopy, I– V, C– V– f and G/ ω– V– f techniques. The surface topography and phase image of the TEA-B film deposited onto p-Si substrate were analyzed by atomic force microscopy. The atomic force microscopy results show a homogenous distribution of boron particles in triethanolamine film. The electronic parameters (barrier height, ideality factor and average series resistance) obtained from I– V characteristics of the diode are 0.81 eV, 2.07 and 5.04 kΩ, respectively. The interface state density of the diode was found to be 2.54 × 10 10 eV − cm −2 under V g = 0. The obtained D it values obtained from C– V and G/ω measurements are in agreement with each other. The profile of series resistance dependent on voltage and frequency confirms the presence of interface states in boron dispersed triethanolamine/p-Si structure. It is evaluated that the boron dispersed triethanolamine controls the electronic parameters and interface properties of conventional Al/p-Si diode.

Localization properties of a tight-binding electronic model on the Apollonian network

An investigation on the properties of electronic states of a tight-binding Hamiltonian on the Apollonian network is presented. This structure, which is defined based on the Apollonian packing problem, has been explored both as a complex network and as a substrate on the top of which physical models can be defined. The Schr\"odinger equation of the model, which includes only nearest-neighbor interactions, is written in a matrix formulation. In the uniform case, the resulting Hamiltonian is proportional to the adjacency matrix of the Apollonian network. The characterization of the electronic eigenstates is based on the properties of the spectrum, which is characterized by a very large degeneracy. The $2\ensuremath{\pi}/3$ rotation symmetry of the network and large number of equivalent sites are reflected in all eigenstates, which are classified according to their parity. Extended and localized states are identified by evaluating the participation rate. Results for other two nonuniform models on the Apollonian network are also presented. In one case, interaction is considered to be dependent of the node degree, while in the other one random on-site energies are considered.

Diffusion and localization in quantum random resistor networks

The theoretical description of transport in a wide class of novel materials is based upon quantum-percolation and related random-resistor-network (RRN) models. We examine the localization properties of electronic states of diverse two-dimensional quantum-percolation models using exact diagonalization in combination with kernel-polynomial-expansion techniques. Employing the local-distribution approach, we determine the arithmetically and geometrically averaged densities of states in order to distinguish extended, current-carrying states from localized ones. To get further insight into the nature of eigenstates of RRN models, we analyze the probability distribution of the local density of states in the whole parameter and energy range. For a recently proposed RRN representation of graphene sheets, we discuss leakage effects.

Synthesis, Structure, Electronic State, and Luminescent Properties of Novel Blue‐Light‐Emitting Aryl‐Substituted 9,9‐Di(4‐(di‐p‐tolyl)aminophenyl)fluorenes

AbstractNovel blue‐light‐emitting fluorene derivatives 5a–c and 7a–c containing bulky and highly emissive groups, namely pyrene, 10‐phenylanthracene‐9‐yl and 10‐(4′‐diphenylaminophenyl)anthracene‐9‐yl groups, as well as hole‐injecting/transporting triarylamines were synthesized. Single crystals of compounds 5a, 5c, 7a, and 7c were grown and their crystal structures were determined by X‐ray diffraction. The four fluorene derivatives have nonplanar molecular structures, which reduce the intermolecular interaction and the likelihood of molecular aggregation or excimer formation. No unwanted long‐wavelength emission was observed in the photoluminescence (PL) spectra of the 5a–c and 7a–c thin films. Their PL spectra reveal excellent thermal stability after annealing treatment under air and ambient light. All of the six compounds show high fluorescence quantum yields and outstanding thermal stabilities. The 2‐aryl and 2,7‐diaryl substituents at the fluorene molecule have a significant effect on the photophysical properties and the thermal characteristics. The six compounds show almost the same energy levels for the highest occupied molecular orbitals (HOMOs) of about −5.20 eV, which allows effective hole injection. The C2‐ and C7‐aryl substituents play a relatively less‐important role in the HOMO energy levels, which depend mainly on the triphenylamino groups at the C9 position. The molecular orbitals, excitation energy, and emission energy were calculated to explain the real origin of their photophysical characteristics. The HOMOs are mainly localized on the triphenylamino groups at the C9 position, while the lowest unoccupied molecular orbitals (LUMOs) have a significant orbital density at the C2‐ and/or C7‐aryl substituents. Pure‐blue‐light‐emitting diodes based on 2,7‐diaryl‐9,9‐di(triarylamino)fluorenes were fabricated.