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  • AIP Publishing  (664,407)
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  • 1
    Online Resource
    Online Resource
    Observation of the predissociated, quasilinear B̃(A′1) state of CHF by optical-optical double resonance
    AIP Publishing ; 2007
    In:  The Journal of Chemical Physics Vol. 126, No. 5 ( 2007-02-07)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 126, No. 5 ( 2007-02-07)
    Abstract: We report the first observation of the predissociative B̃ state of a halocarbene molecule. Rovibronic energy levels were measured in the B̃(A′1) state of CHF by fluorescence dip detected optical-optical double resonance spectroscopy via the à state. The origin was found to lie 30817.4cm−1 above the zero point level of the X̃ state. Rotational transitions within six purely bending states, and states involving one or two quanta of CF-stretch were observed, including the vibrational angular momentum components. Interpretation of the spectrum, with support of ab initio calculations, shows that CHF is quasilinear in the B̃ state with a small (−200cm−1) barrier to linearity which lies below the zero-point level. The rotational constant, B=1.04 to 1.09cm−1, depending on vibrational state, again in good agreement with theory. All observed B̃ state levels were predissociative, as evidenced by Lorentzian line broadening. Linewidths varied with initial state from 0.7–10.8cm−1, corresponding to excited state lifetimes of 0.5–8ps.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.2515273
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2007
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 2
    Online Resource
    Online Resource
    The effect of active layer thickness and composition on the performance of bulk-heterojunction solar cells
    AIP Publishing ; 2006
    In:  Journal of Applied Physics Vol. 100, No. 9 ( 2006-11-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 100, No. 9 ( 2006-11-01)
    Abstract: At present, bulk heterojunction polymer solar cells are typically fabricated with an active layer thickness of between 80 and 100nm. This active layer thickness has traditionally been chosen based on convenience and empirical results. However, a detailed study of the effects that active layer thickness has on the short circuit current and efficiency has not been performed for bulk heterojunction polymer solar cells so far. We demonstrate that the performance of these devices is highly dependent on the active layer thickness and, using a well established model for optical interference, we show that such effects are responsible for the variations in performance as a function of active layer thickness. We show that the ideal composition ratio of the donor and acceptor materials is not static, but depends on the active layer thickness in a predictable manner. A comparison is made between solar cells comprised of the donor materials regioregular poly(3-hexylthiophene) and poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-p-phenylenevinylene) with the acceptor [6, 6]-phenyl C61-butyric acid methyl ester to show that our results are not material specific and that high efficiency solar cells can be fabricated with active layer thickness greater than 100nm for both material mixtures. Finally, a device with an active layer thickness of 225nm is fabricated with a power efficiency of 3.7% under AM1.5 illumination at an intensity of 100mW∕cm2.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.2360780
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2006
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 3
    Online Resource
    Online Resource
    N, NH, and NH2 radical densities in a remote Ar–NH3–SiH4 plasma and their role in silicon nitride deposition
    AIP Publishing ; 2006
    In:  Journal of Applied Physics Vol. 100, No. 9 ( 2006-11-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 100, No. 9 ( 2006-11-01)
    Abstract: The densities of N, NH, and NH2 radicals in a remote Ar–NH3–SiH4 plasma used for high-rate silicon nitride deposition were investigated for different gas mixtures and plasma settings using cavity ringdown absorption spectroscopy and threshold ionization mass spectrometry. For typical deposition conditions, the N, NH, and NH2 radical densities are on the order of 1012cm−3 and the trends with NH3 flow, SiH4 flow, and plasma source current are reported. We present a feasible reaction pathway for the production and loss of the NHx radicals that is consistent with the experimental results. Furthermore, mass spectrometry revealed that the consumption of NH3 was typically 40%, while it was over 80% for SiH4. On the basis of the measured N densities we deduced the recombination and sticking coefficient for N radicals on a silicon nitride film. Using this sticking coefficient and reported surface reaction probabilities of NH and NH2 radicals, we conclude that N and NH2 radicals are mainly responsible for the N incorporation in the silicon nitride film, while Si atoms are most likely brought to the surface in the form of SiHx radicals.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.2358330
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2006
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 4
    Online Resource
    Online Resource
    Stability of rocksalt phase of zinc oxide under strong compression: Synchrotron x-ray diffraction experiments and first-principles calculation studies
    AIP Publishing ; 2006
    In:  Journal of Applied Physics Vol. 100, No. 9 ( 2006-11-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 100, No. 9 ( 2006-11-01)
    Abstract: The stability of rocksalt (B1) phase of ZnO under high pressure up to 2Mbars was studied using angular dispersive x-ray diffraction at room temperature and compared to the structurally analogous CdO where both theoretical and experimental results are available. First-principles total energy calculations predict the B1-to-B2 (CsCl-type) phase transition in ZnO and CdO to occur at 261 and 83GPa, respectively. The bulk moduli, K0, of the B1 structure of ZnO were measured and the possible high pressure CsCl-type (B2) structure was looked for. The potential application of ZnO as an internal pressure marker in x-ray diffraction study at the megabar range is proposed.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.2357644
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2006
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 5
    Online Resource
    Online Resource
    The electronic properties of amorphous and crystallized In2O3 films
    AIP Publishing ; 2006
    In:  Journal of Applied Physics Vol. 100, No. 9 ( 2006-11-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 100, No. 9 ( 2006-11-01)
    Abstract: Polycrystalline In2O3 films with high crystallinity were prepared by annealing the amorphous In2O3 films deposited at room temperature by using dc/rf sputtering method. General electronic behaviors of both these amorphous and polycrystalline films have been investigated by means of Hall effect and resistivity measurements at temperatures between 4.2 and 300K. For the amorphous films, ionized impurity scattering dominates the electronic transport, and Hall mobility agrees well with the theory of degenerate semiconductors with divalent impurity scattering centers. On the other hand, the conduction mechanism of the polycrystalline films is governed dominantly by phonon scattering, since these films exhibit a clearly positive temperature coefficient of resistivity with the maximum Hall mobility of 150cm2∕Vs at 300K and 230cm2∕Vs at 4.2K, with little change in carrier concentration between these temperatures. Conductivity of both the amorphous and polycrystalline films is found to show a linear relationship in a double-logarithmic plot against carrier concentration between 4×1015 and 5×1020cm−3, a typical behavior of the impurity semiconductors with parabolic conduction band. For each set of films with the same thermal history, Hall mobility is found to vary on a convex upward curve with respect to carrier concentration. This behavior suggests a general and strong correlation of the structural defects introduced upon deposition and localization of conduction electrons with electron mobility, which led to a proposition of three categories for temperature coefficient of resistivity with major transport mechanisms of phonon scattering, divalent impurity scattering, and weak localization, respectively.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.2358829
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2006
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 6
    Online Resource
    Online Resource
    Magnetic reconfiguration of MnAs∕GaAs(001) observed by magnetic force microscopy and resonant soft x-ray scattering
    AIP Publishing ; 2006
    In:  Journal of Applied Physics Vol. 100, No. 8 ( 2006-10-15)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 100, No. 8 ( 2006-10-15)
    Abstract: We investigated the thermal evolution of the magnetic properties of MnAs epitaxial films grown on GaAs(001) during the coexistence of hexagonal/orthorhombic phases using polarized resonant (magnetic) soft x-ray scattering and magnetic force microscopy. The results of the diffuse satellite x-ray peaks were compared to those obtained by magnetic force microscopy and suggest a reorientation of ferromagnetic terraces as temperature rises. By measuring hysteresis loops at these peaks we show that this reorientation is common to all ferromagnetic terraces. The reorientation is explained by a simple model based on the shape anisotropy energy. Demagnetizing factors were calculated for different configurations suggested by the magnetic images. We noted that the magnetic moments flip from an in-plane monodomain orientation at lower temperatures to a three-domain out-of-plane configuration at higher temperatures. The transition was observed when the ferromagnetic stripe width L is equal to 2.9 times the film thickness d. This is in good agreement with the expected theoretical value of L=2.6d.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.2356794
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2006
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 7
    Online Resource
    Online Resource
    Hydrogen-bond assisted enormous broadening of infrared spectra of phenol-water cationic cluster: An ab initio mixed quantum-classical study
    AIP Publishing ; 2007
    In:  The Journal of Chemical Physics Vol. 126, No. 7 ( 2007-02-21)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 126, No. 7 ( 2007-02-21)
    Abstract: The infrared spectrum of phenol-water cationic cluster, [PhOH∙H2O]+, taken by Sawamura et al. [J. Phys. Chem. 100, 8131 (1996)] is puzzling in that the peak due to the stretching mode of the phenolic OH (3657cm−1 for a neutral monomer and 3524cm−1 for PhOH∙H2O) seemingly disappears and instead an extremely broad tail extending down to 2900cm−1 is observed. The present authors theoretically ascribe this anomalous spectrum to an inhomogeneous broadening of the OH stretching peak caused by the hydrogen bond, the strength of which has been greatly enhanced by ionization of the phenyl ring. Indeed they estimate that the peak position is at 2300cm−1 and the spectral width can become as wide as 1000cm−1 at the cluster energy of 32kcal∕mol. This surprisingly wide broadening can be generic in hydrogen-bond systems, which in turn is useful to study the nature of the hydrogen-bond assisted dynamics in various systems such as those in DNA and proteins. To study the present system quantitatively, the authors have developed an ab initio mixed quantum-classical method, in which the nuclear motions on an adiabatic ab initio potential surface are treated such that only the OH stretching motion is described quantum mechanically, while all the other remaining modes are treated classically with on-the-fly scheme. This method includes the implementation of many numerical methodologies, which enables it to deal with a relatively large molecular system. With this theoretical method, the authors analyze the present anomalous broadening in a great detail. In particular, they suggest that one can extract direct information about the hydrogen-bond dynamics with respect to the clear correlation between the vibrational excitation energy of the OH stretching and intermolecular distance by means of a time-resolved infrared spectroscopy: Reflecting the slow and wide-range variation of the intermolecular distance of the relevant hydrogen bond, the time-resolved spectrum is predicted to vary (shift) largely covering the wide range of frequency domain. Thus, it is found that the short-time average along a selected trajectory sensitively reflects the change of the intermolecular distance. The authors also study the effect of internal energy on the hydrogen bonding and the OH spectrum.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.2434778
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2007
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 8
    Online Resource
    Online Resource
    Morphology and electronic properties of the pentacene on cobalt interface
    AIP Publishing ; 2006
    In:  Journal of Applied Physics Vol. 100, No. 9 ( 2006-11-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 100, No. 9 ( 2006-11-01)
    Abstract: In this paper, we report the structural and electronic properties of pentacene thin films grown on a polycrystalline Co film using atomic force microscopy and ultraviolet photoemission spectroscopy (UPS), respectively. Investigation of this type of interface is of importance for the engineering of hybrid organometallic spintronic devices for which the use of spin polarized electrodes is a prerequisite. Uniform single crystalline areas of pentacene as large as several micrometers, with molecules arranging almost perpendicular to the substrate, were obtained. For the electronic properties at this interface, we have found an energy barrier for the hole injection of about 1eV, in spite of the fact that the ionization potential of pentacene reported previously equals the work function of Co. A shift of the vacuum level of the same magnitude has also been observed. A comparison of the UPS spectra of the pentacene films with the gas phase spectrum directly indicates that hybridization effects are present at this interface.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.2363707
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2006
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 9
    Online Resource
    Online Resource
    Average excitation energies from time-dependent density functional response theory
    AIP Publishing ; 2007
    In:  The Journal of Chemical Physics Vol. 126, No. 7 ( 2007-02-21)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 126, No. 7 ( 2007-02-21)
    Abstract: The authors present an occupation number averaging scheme for time-dependent density functional response theory (TD-DFRT) in frequency domain. The known problem that TD-DFRT within the local (spin) density approximation (LDA/LSDA) inaccurately predicts Rydberg and charge-transfer excitation energies has been reexamined from the methodology of linear response, without explicit correction of the exchange-correlation potential. The working equations of TD-DFRT are adapted to treat arbitrary difference of orbital occupation numbers, using the nonsymmetric matrix form of Casida’s formulation of TD-DFRT [M. E. Casida, in Recent Advances in Density Functional Methods, edited by D. P. Chong (World Scientific, Singapore, 1995), Pt. I, p. 155]. The authors’ scheme is applied to typical closed-shell and open-shell molecular systems by examining the dependence of excitation energies on the fraction of excited electron. Good performance of this modified linear response scheme is shown, and is consistent with the authors’ previous examination by the real-time propagation approach, suggesting that the calculation of average excitation energies might be one of the ways to better decode excitation energies from LDA/LSDA. Different techniques for treating singlet, triplet, and doublet states are discussed.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.2436887
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2007
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 10
    Online Resource
    Online Resource
    Characteristics of InGaPN∕GaAs heterostructures investigated by photoreflectance spectroscopy
    AIP Publishing ; 2006
    In:  Journal of Applied Physics Vol. 100, No. 9 ( 2006-11-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 100, No. 9 ( 2006-11-01)
    Abstract: Photoreflectance (PR) spectra at various temperatures and photoluminescence (PL) spectra and high-resolution x-ray rocking curve (XRC) measurements are used to investigate the band alignment, epitaxial-strain, and atomic-ordering effects in In0.54Ga0.46P1−yNy∕GaAs (y=0%–2.0%) heterostructures. The existence of additional peaks in PR spectra at higher levels of nitrogen (N) incorporation implies that the band alignment switches from type I to type II, due to the lowering of the conduction band. The electric field at the interface is determined and is discussed with the N content. Redshifts of the PR and PL peaks indicate that the band gap of InGaPN is dramatically reduced as N is incorporated. The valence-band splitting (VBS) and the spin-orbit splitting of InGaPN are obtained from PR spectra. High-resolution XRC measurements indicate that as the N content increases, the lattice mismatch and the compressive strain between the epilayer and GaAs substrate decrease while the VBS increases, which implies an increase in the degree of ordering in InGaPN caused by the transition from a cubic zinc blende structure to a [111] CuPt structure. The order parameter η of InGaPN deduced from the VBS ranges from 0.256 to 0.498, indicating that the InGaPN epilayer becomes more ordered with increasing N incorporation.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.2358327
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2006
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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