Showing papers on "Stark effect published in 2008"
TL;DR: In this article, the authors showed that the gap of BN nanoribbons with zigzag or armchair edges can be significantly reduced by a transverse electric field and be completely closed at a critical field which decreases with increasing ribbon width.
Abstract: Systematic ab initio calculations show that the energy gap of BN nanoribbons (BNNRs) with zigzag or armchair edges can be significantly reduced by a transverse electric field and be completely closed at a critical field which decreases with increasing ribbon width. In addition, a distinct gap modulation in the ribbons with zigzag edges is presented when a reversed electric field is applied. In a weak field, the gap reduction of the BNNRs with zigzag edges originates from the field-induced energy level shifts of the spatially separated edge states, while the gap reduction of the BNNRs with armchair edges arises from the Stark effect. As the field gets stronger, the energy gaps of both types of the BNNRs gradually close due to the field-induced motion of nearly free electron states. Without the applied fields, the energy gap modulation by varying ribbon width is rather limited.
293 citations
TL;DR: It turned out that the interactions of water molecules with nitrogen atom's lone pair orbital and with nitrile pi orbitals can be well described by the electrostatic potential calculation method.
Abstract: Hydration effects on the CN stretching mode frequencies of MeCN and MeSCN are investigated by carrying out ab initio calculations for a number of MeCN-water and MeSCN-water complexes with varying number of water molecules. It is found that the CN frequency shift induced by the hydrogen-bonding interactions with water molecules originate from two different ways to form hydrogen bonds with the nitrogen atom of the CN group. Considering the MeCN- and MeSCN-water cluster calculation results as databases, we first examined the validity of vibrational Stark effect relationship between the CN frequency and the electric field component parallel to the CN bond and found no strong correlation between the two. However, taking into account of additional electric field vector components is a simple way to generalize the vibrational Stark theory for the nitrile chromophore. Also, the electrostatic potential calculation method has been proposed and examined in detail. It turned out that the interactions of water molecu...
170 citations
Abstract: Ab initio calculations reveal a universal scaling law on how the electronic structure of boron nitride (BN) nanoribbons and nanotubes is modified by a transverse electric field Due to the structural symmetry difference, the energy gap of zigzag BN ribbons can be reduced or increased by the electric field depending on the sign of the field, while that of the armchair ones is always reduced However, the linear giant Stark effect coefficients of zigzag and armchair BN nanoribbons, as well as those of BN nanotubes, are found to obey a unified scaling law where the coefficient increases linearly with the ribbon width or the tube diameter with a slope of 10 The mechanism of the scaling law is identified using a general model, which may be applicable to other semiconducting nanostructures
102 citations
TL;DR: The effects of hydrogen bonding of amino acid side chains to the nitrile probe are considered, and applications of vibrational Stark effect spectroscopy to investigations of ligand binding and biological function are discussed.
Abstract: Vibrational Stark effect spectroscopy was used to measure electrostatic fields in the hydrophobic region of the active site of human aldose reductase (hALR2). A new hALR2 inhibitor was designed and synthesized that contains a nitrile probe with a Stark tuning rate of 0.77 cm-1/(MV/cm). Mutations to amino acid residues in the vicinity of the nitrile functional group were selected based on electrostatics calculations, possible complications from hydrogen bonds near the nitrile, and comparison with the active site of human aldehyde reductase, whose structure is very similar. Changes in the absorption energy of the nitrile probe when bound to those mutated proteins were then used to quantify perturbations to the protein's electrostatic field. Electrostatic field changes as large as −10 MV/cm were observed. Measured electrostatic fields were compared to predictions based on continuum electrostatics calculations, revealing that substantial modifications to the calculation strategy are necessary. The effects of ...
96 citations
TL;DR: In this article, the spectral distance between forbidden and allowed components was calculated for dielectric barrier discharge in helium and the spectral distribution of electric field strength was determined from the Stark splitting and shifting of two visible helium lines and their forbidden components.
Abstract: Spatial distribution of electric field strength in dielectric barrier discharge in helium is determined from the Stark splitting and shifting of two visible helium lines and their forbidden components. Electric field is calculated by using spectral distance between forbidden and allowed components and results are compared to those obtained by using forbidden/allowed intensity ratio. Distributions of electric field, obtained for 200 and 800 mbar pressures, are typical for the glow mode of the discharge.
81 citations
TL;DR: In this article, the authors acquired spectrally resolved images of a laser-induced breakdown spectroscopy plasma generated in air on an aluminum target by irradiation with the Nd:YAG fundamental emission.
77 citations
TL;DR: Numerical propagation modeling of the optical Stark effect confirms that this mechanism is able to form the pulses that are generated directly by an optical Stark passively mode-locked semiconductor disk laser at a 1 GHz repetition rate.
Abstract: We report on 260 fs transform-limited pulses generated directly by an optical Stark passively mode-locked semiconductor disk laser at a 1 GHz repetition rate. A surface recombination semiconductor saturable absorber mirror and a step-index gain structure are used. Numerical propagation modeling of the optical Stark effect confirms that this mechanism is able to form the pulses that we observe.
74 citations
TL;DR: In this article, a broad photoluminescence band with a large Stokes shift is observed, and its decay time depends strongly on the emission energies, attributed to radiative recombination of photo-excited carriers after multiple-step hopping among deep trapping sites on nanoparticle surfaces.
69 citations
TL;DR: In this article, the authors proposed more accurate values for key parameters such as effective masses and band offsets that are required for device design, based on photocurrent electroabsorption experiments on different samples and fitting of the resulting allowed and forbidden transitions.
Abstract: Germanium (Ge) and silicon-germanium (Si-Ge) have the potential to integrate optics with Si IC technology. The quantum-confined Stark effect, a strong electroabsorption mechanism often observed in III-V quantum wells (QWs), has been demonstrated in Si-Ge/Ge QWs, allowing optoelectronic modulators in such group IV materials. Here, based on photocurrent electroabsorption experiments on different samples and fitting of the resulting allowed and nominally forbidden transitions, we propose more accurate values for key parameters such as effective masses and band offsets that are required for device design. Tunneling resonance modeling including conduction band nonparabolicity was used to fit the results with good consistency between the experiments and the fitted transitions.
65 citations
TL;DR: The photocurrent peak corresponding to the ground state exciton increases by a factor of 200 beyond a critical electric field, and shows both red and blue shifts depending on the field regime, providing evidence for field-induced mixing between excitonic and free carrier states.
Abstract: The field-dependent photocurrent spectrum of individual carbon nanotubes is measured using a displacement photocurrent technique. A series of peaks is observed in the photocurrent corresponding to both excitonic and free carrier transitions. The photocurrent peak corresponding to the ground state exciton increases by a factor of 200 beyond a critical electric field, and shows both red and blue shifts depending on the field regime. This provides evidence for field-induced mixing between excitonic and free carrier states.
64 citations
TL;DR: In this paper, the authors performed Fourier transform microwave spectroscopy of benzonitrile, without and with applied electric fields, and derived accurate values for the rotational constants, centrifugal distortion constants, and nitrogen nuclear quadrupole coupling constants.
TL;DR: In this paper, the authors demonstrate the control of the quantum-confined Stark effect in InGaN∕GaN quantum wells (QWs), grown along the [0001] direction as part of the active region of visible light emitting diodes (LEDs).
Abstract: We demonstrate the control of the quantum-confined Stark effect in InGaN∕GaN quantum wells (QWs), grown along the [0001] direction as part of the active region of visible light emitting diodes (LEDs). The effect can be altered by modifying the strain applied to the active region by the hole injection and contact layers. The optical characteristics and electrostatic potentials of the active region of the visible LEDs with different p-type layers are compared. LEDs with p-InGaN on top of the active region show a reduced blueshift in the peak wavelength with increasing injection current and a lower potential difference across the QW than those with p-GaN layers. The electrostatic potentials across the QW have estimated average values of ∼0.8 and ∼1.3MV∕cm for the active region of LEDs of current study with p-InGaN and p-GaN layers, respectively.
TL;DR: In this paper, a spectroscopic analysis of a filament generated by a femtosecond laser pulse in air was performed and the characteristic Stark broadened atomic oxygen triplet centered at 777.4 nm was observed.
TL;DR: In this paper, the effect of a control beam on a Lambda electromagnetically induced transparency (EIT) system in 87Rb has been studied, where the control beam couples one ground state to another excited state forming a four level N-system.
Abstract: We study the effect of a control beam on a Lambda electromagnetically induced transparency (EIT) system in 87Rb. The control beam couples one ground state to another excited state forming a four level N-system. Phase coherent beams to drive the N-system are produced using a double injection scheme. We show that the control beam can be used to Stark shift or split the EIT resonance. Finally, we show that the when the control beam is on-resonance one observes a Doppler-free and sub-natural absorptive resonance with a width of order 100 kHz. Crucially, this narrow absorptive resonance only occurs when atoms with a range of velocities are present, as is the case in a room temperature vapour.
TL;DR: A potential buildup in front of a magnetized cascaded arc hydrogen plasma source is explored via E x B rotation and plate potential measurements and asymmetric spectra are observed.
Abstract: A potential buildup in front of a magnetized cascaded arc hydrogen plasma source is explored via $\stackrel{P\vec}{E}\ifmmode\times\else\texttimes\fi{}\stackrel{P\vec}{B}$ rotation and plate potential measurements. Plasma rotation approaches thermal speeds with maximum velocities of $10\phantom{\rule{0.3em}{0ex}}\mathrm{km}∕\mathrm{s}$. The diagnostic for plasma rotation is optical emission spectroscopy on the Balmer-$\ensuremath{\beta}$ line. Asymmetric spectra are observed. A detailed consideration is given on the interpretation of such spectra with a two distribution model. This consideration includes radial dependence of emission determined by Abel inversion of the lateral intensity profile. Spectrum analysis is performed considering Doppler shift, Doppler broadening, Stark broadening, and Stark splitting.
TL;DR: In this paper, the excitation energies of ns, np, nd, and nf (n{<=}6) states in neutral lithium are evaluated within the framework of relativistic many-body theory.
Abstract: The excitation energies of ns, np, nd, and nf (n{<=}6) states in neutral lithium are evaluated within the framework of relativistic many-body theory. First-, second-, third-, and all-order Coulomb energies and first- and second-order Breit corrections to energies are calculated. All-order calculations of reduced matrix elements, oscillator strengths, transition rates, and lifetimes are given for levels up to n=4. Electric-dipole (2s-np), electric-quadrupole (2s-nd), and electric-octupole (2s-nf), matrix elements are evaluated to obtain the corresponding ground-state multipole polarizabilities using the sum-over-states approach. Scalar and tensor polarizabilities for the 2p{sub 1/2} and 2p{sub 3/2} states are also calculated. Magnetic-dipole hyperfine constants A are determined for low-lying levels up to n=4. The quadratic Stark shift for the (F=2 M=0){r_reversible}(F=1 M=0) ground-state hyperfine transition is found to be -0.0582 Hz/(kV/cm){sup 2}, in slight disagreement with the experimental value -0.061{+-}0.002 Hz/(kV/cm){sup 2}. Matrix elements used in evaluating polarizabilities, hyperfine constants, and the quadratic Stark shift are obtained using the all-order method.
TL;DR: This work describes the implementation and recent results from the motional Stark effect (MSE) collisionally induced fluorescence diagnostic on NSTX, with improvements the polarization fraction is approximately 30%-40% and, combined with the large throughput, a time resolution of approximately 5 ms.
Abstract: This work describes the implementation and recent results from the motional Stark effect (MSE) collisionally induced fluorescence diagnostic on NSTX. Due to the low magnetic field on NSTX the MSE diagnostic requires a new approach for the viewing optics and spectral filter. This has been accomplished with a novel optical design that reduces the geometric Doppler broadening, and a high throughput, high resolution spectral filter to optimize signal-to-noise ratio. With these improvements the polarization fraction is ∼30%–40% and, combined with the large throughput, a time resolution of ∼5 ms. The MSE diagnostic presently has 16 sight lines operating, providing measurements of the magnetic field line pitch from the plasma center to near the outboard edge of the plasma.
TL;DR: In this paper, the crystal-field split energy levels of the 7 F J and 5 D 4 of TbAlO 3+ in stoichiometric single crystals of ortho-aluminate TbN 3 have been analyzed.
TL;DR: In this paper, the authors used an all-electrical technique to populate and control a single-photon emitting state, and filter out dephasing by shifting the emission energy on time scales below the dephase time of the state.
Abstract: We generate indistinguishable photons from a semiconductor diode containing an InGaAs/GaAs quantum dot. By using an all-electrical technique to populate and control a single-photon emitting state, we filter out dephasing by Stark shifting the emission energy on time scales below the dephasing time of the state. By mixing consecutive photons on a beam splitter, we observe two-photon interference with a visibility of 64%.
TL;DR: In this article, a very early plasma dynamics (first 100 ns) using direct plasma imaging, light scattering, and transmission measurements from a synchronized 532-nm probe laser pulse was studied.
TL;DR: In this paper, a two-colour vibrational sum-frequency generation (2C-SFG) set-up based on the CLIO free electron laser synchronized with a tuneable visible laser source is used to probe simultaneously the vibrational and electronic fingerprint of a thiophenol/Ag(1.1) interface.
TL;DR: In this paper, the effect of a lateral electric field on the optical properties of a single deterministically positioned InAs/InP quantum dot was examined, and it was shown that the ground-state excitonic Stark shift is significantly reduced in comparison with the single-particle picture.
Abstract: We examine the effect of a lateral electric field on the optical properties of a single deterministically positioned InAs/InP quantum dot. We show experimentally that the ground-state excitonic Stark shift is significantly reduced in comparison with the single-particle picture and that the lateral electric field introduces a new previously forbidden optical transition. Results of full configuration-interaction calculations show that the Coulomb interactions of electrons and holes are modified by the electric field leading to the compensation of the single-particle Stark shift. The calculations also account for the appearance of the field-activated optical transition as an excitonic recombination event. The comparison of exciton and predicted charged exciton spectra allows us to exclude the presence of charged exciton complexes within the measured emission spectra. The ability to precisely position a single quantum dot and demonstrate control over the electronic properties of such a dot is expected to find application in scalable techniques for quantum information science.
TL;DR: In this article, a simple analytical method for an approximate calculation of line shapes of highly excited (Rydberg) atoms and ions is proposed, where a very good accuracy is achieved over a range of transitions, species and plasma parameters.
Abstract: Calculations of line shapes of highly excited (Rydberg) atoms and ions are important for many topics in plasma physics and astrophysics. However, the Stark broadening of the radiative transitions originating from high-n levels of hydrogen or hydrogen-like ions is rather complex, making the detailed calculations of their spectral structure very cumbersome. Here, we suggest a simple analytical method for an approximate calculation of such line shapes. The utility of the method is demonstrated in application to the line broadening in plasma, where a very good accuracy is achieved over a range of transitions, species and plasma parameters.
TL;DR: In this article, the Stark effect measurements for alizarin, both free in solution and adsorbed to TiO2 nanoparticles, have been addressed whether the excited-state orbital of adsorbated alizinates extends into the solid and involves the orbitals of the Ti atom or remains localized within the alizaran molecule.
Abstract: Alizarin is one of the dyes extensively investigated as an example of a molecule capable of serving as a light absorber and an electron donor in model systems designed for the new type solar cells. Using the Stark effect measurements for alizarin, both free in solution and adsorbed to TiO2 nanoparticles, the question has been addressed whether the excited-state orbital of adsorbed alizarin extends into the solid and involves the orbitals of the Ti atom or remains localized within the alizarin molecule. Because an important role can be played by the electric field at the charged surface of the nanoparticles, the field was modulated by changing the pH of the medium. The results reveal a substantial dipole moment change on the electronic excitation of the alizarin−TiO2 system, |Δμ| ≈ 10 Debye units or slightly more. The observed dependence of the absorption maximum and the measured |Δμ| on pH were used to distinguish between Δμ directed toward the nanoparticle surface and that corresponding to the intrinsic ...
TL;DR: In this article, a nanosecond pulsed frequency doubling Nd:YAG (532 nm) laser-induced breakdown spectroscopy of silicon was performed using a Nd-YAG laser and the temporal evolution of the laser ablation plumes in air at atmospheric and ambient pressure of ∼10−5 mbar was presented.
TL;DR: The experiment together with the calculations reveals information on the photochemistry of the HXeCCH molecule and the interpretation of the experimental findings has been supported by ab initio calculations.
Abstract: We report on the first observation of the organoxenon HXeCCH molecule in the gas phase. This molecule has been prepared in a molecular beam experiment by 193nm photolysis of an acetylene molecule on Xen clusters (n¯≈390). Subsequently the molecule has been oriented via the pseudo-first-order Stark effect in a strong electric field of the polarized laser light combined with the weak electrostatic field in the extraction region of a time-of-flight spectrometer. The experimental evidence for the oriented molecule has been provided by measurements of its photodissociation. For comparison, photolysis of C2H2 on Arn clusters (n¯≈280) has been measured. Here the analogous rare gas molecule HArCCH could not be generated. The interpretation of our experimental findings has been supported by ab initio calculations. In addition, the experiment together with the calculations reveals information on the photochemistry of the HXeCCH molecule. The 193nm radiation excites the molecule predominantly into the 2Σ+1 state, wh...
TL;DR: In this paper, the Stark widths of 34 spectral lines of Pb I have been measured in a Laser-Induced-Plasma (LIP), and the optical emission spectroscopy from a LIP generated by a 10 −640 Ã A radiation, with an irradiance of 1.4 × 10 10 Ã W cm − 2 on a Sn −Pb target in an atmosphere of argon was analyzed between 1900 and 7000 Ã.
TL;DR: The treatment of the previous paper is extended to molecular wires and the effect of electron-vibrational interactions on the electronic transport induced by femtosecond omega+2omega laser fields along unbiased molecular nanojunctions is investigated.
Abstract: The treatment of the previous paper is extended to molecular wires. Specifically, the effect of electron-vibrational interactions on the electronic transport induced by femtosecond ω+2ω laser fields along unbiased molecular nanojunctions is investigated. For this, the photoinduced vibronic dynamics of trans-polyacetylene oligomers coupled to macroscopic metallic leads is followed in a mean-field mixed quantum-classical approximation. A reduced description of the dynamics is obtained by introducing projective lead-molecule couplings and deriving an effective Schrodinger equation satisfied by the orbitals in the molecular region. Two possible rectification mechanisms are identified and investigated. The first one relies on near-resonance photon-absorption and is shown to be fragile to the ultrafast electronic decoherence processes introduced by the wire’s vibrations. The second one employs the dynamic Stark effect and is demonstrated to be highly efficient and robust to electron-vibrational interactions.
TL;DR: In this paper, the optical properties of Er3+ in polycrystalline (ceramic), and nanocrystalline forms of cubic (bixbyite) yttrium oxide are modeled based on the absorption spectra obtained between 400 and 1700 nm and the fluorescence spectra observed between 1500 and 1670 nm.
Abstract: The optical properties of Er3+ in polycrystalline (ceramic), and nanocrystalline forms of cubic (bixbyite) yttrium oxide are modeled based on the absorption spectra obtained between 400 and 1700 nm and the fluorescence spectra observed between 1500 and 1670 nm. Both spectra were obtained at 8 K. The observed crystal-field splitting and the measured intensities of transitions between Stark levels of the L2S+1J multiplet manifolds of Er3+(4f11) in both the C2 and C3i sites of Y2O3 are analyzed in terms of established models. The inversion symmetry of C3i sites limits the observed electronic transitions to magnetic dipole transitions between the I413/2 and I415/2 manifolds. There is no spectroscopic evidence for transitions involving other multiplet manifolds of Er3+ ions in C3i sites. For Er3+ ions in C2 sites, forced electric dipole transitions are allowed between the J+12 Stark levels associated with each manifold. With few exceptions, the crystal-field splitting and the intensities of the transitions bet...
TL;DR: In this article, the authors report on semipolar GaN/AlN multiple-quantum-well structures grown on m-plane sapphire by plasma-assisted molecular-beam epitaxy.
Abstract: We report on semipolar GaN/AlN multiple-quantum-well structures grown on m-plane sapphire by plasma-assisted molecular-beam epitaxy. Optical investigation confirms a significant reduction in the quantum-confined Stark effect, in agreement with theoretical calculations, which predict an internal electric field between 0.6 and −0.55 MV/cm in the quantum wells, depending on the strain state. With respect to polar materials, the reduction in the internal electric field results in a substantial redshift of the intersubband energy.