Cu-Ni castings and wrought pipes nominally contain 1% Fe to 2% Fe, which is added to improve the ... more Cu-Ni castings and wrought pipes nominally contain 1% Fe to 2% Fe, which is added to improve the Cu-Ni alloy's erosioncorrosion resistance. After fabrication, Cu-Ni products are solution heat-treated to dissolve the iron uniformly andform a single-phase alloy. During welding, however, iron can precipitatefrom solid solution onto grain boundaries in the heat-alfected zones (HAZ). During seawater service, these iron-rich precipitates can dissolve preferentially (galvanically), leading to intergranular corrosion of the HAZ. The present report described 90-10 Cu-Ni alloys in which different soluble elements were substitutedfor iron. Jetimpingement testing in filtered natural seawater showed that 2% In also promoted improved erosion-eorrosion resistance. Because indium is very soluble in copper, it should not precipitate in the HAZ dUring welding and cause intergranular corrosion of the HAZ dUring seawater service. The present study reviewed the literature on the mechanisms by which iron is believed to improve the erosion-eorrosion resistance, and proposed a different model based on doping of the thin surface oxidefzlm.
The recent convergence of chiral molecules with metal halide perovskite frameworks gives rise to ... more The recent convergence of chiral molecules with metal halide perovskite frameworks gives rise to an interesting family of chiral systems: two-dimensional, chiral hybrid organic−inorganic perovskites (chiral-HOIPs). While possessing photovoltaic properties of traditional HOIPs, this class of materials is endowed with chirality through its organic ligands in which the degeneracy of the electron spin in charge transport is broken. That is, the chirality-induced spin selectivity (CISS) effect manifests, making it a promising platform to bridge optospintronic studies and the CISS effect. In this work, chiral-HOIP/NiFe heterostructures are studied by means of the magneto-optical Kerr effect using a Sagnac interferometer. Upon illumination of the chiral-HOIPs, the Kerr signal at the chiral-HOIP/NiFe interface changes, and a linear dependence of the response on the magnetic field is observed. The sign of the slope was found to depend on the chirality of the HOIPs. The results demonstrate the utility of chiral-HOIP materials for chiral opto-spintronic applications.
Different conformers for meta-methylstilbenes cause nonexponential decay of the trans excited sta... more Different conformers for meta-methylstilbenes cause nonexponential decay of the trans excited state. The decay kinetics of these molecules is used to explore the nature of the reaction coordinate.
Experimental studies of the time-resolved bangap emission of CdSe are used to probe the attribute... more Experimental studies of the time-resolved bangap emission of CdSe are used to probe the attributes required in a theoretical model for the carrier dynamics of semiconductor electrodes. By variation of excitation conditions and material properties, the validity of approximations in a commonly used model are tested. The experimental results show that the details of bulk recombination, the effects of self-absorption, and the influence of the space charge field are quite important factors for the carrier dynamics. Simulation results show that the detailed kinetics of the interfacial recombination can also have important consequences for the carrier relaxation. Appropriate modeling of these processes is needed before a surface recombination velocity can be extracted from such studies in a quantitative manner. 43 refs., 9 figs., 2 tabs.
Optical transmission through subwavelength nanoaperture arrays can be modulated by metallic nanop... more Optical transmission through subwavelength nanoaperture arrays can be modulated by metallic nanoparticles that are nested in the nanoaperture. The localized surface plasmon resonance of nanoparticles can strongly modulate and in some cases dominate the transmission.
The rate of photoisomerization of 4,4‐dimethoxystilbene has been studied in two solvent series. T... more The rate of photoisomerization of 4,4‐dimethoxystilbene has been studied in two solvent series. These studies reveal that a separation of solvent and intramolecular effects is possible in the n‐alkanes, but not the n‐alcohols. The experimental results are interpreted in terms of the dynamical solvent response.
Journal of Physical Chemistry Letters, Oct 11, 2018
photoluminescence in doped tin dioxide [Sn(Ln)O 2 ] and doped titanium dioxide [Ti(Ln)O 2 ] nanop... more photoluminescence in doped tin dioxide [Sn(Ln)O 2 ] and doped titanium dioxide [Ti(Ln)O 2 ] nanoparticles shows that the emission efficiency of trivalent lanthanide cations (Ln 3+) in an oxide matrix can be improved by change of the cation site symmetry. An analysis of Ln 3+ emission quantum yield and asymmetry ratio is used to identify the importance of symmetry breaking around the dopant site for enhancing the Ln 3+ emission intensity. These findings identify an important criterion for engineering the luminescence intensity of dopant ions in semiconductor nanoparticle-based luminophores, which goes beyond the primary criterion of engineering the relative positions of the dopant energy levels with respect to the band edges of the host nanoparticle matrix.
... recommend 5.3 mg/m3 as the 15-min exposure limit.25 However, the hexadecanethiol SAM on a car... more ... recommend 5.3 mg/m3 as the 15-min exposure limit.25 However, the hexadecanethiol SAM on a carefully rinsed sur-face was in ... This work was funded by Liz Claiborne Accesso-ries, Inc., and Waldeck and Gu acknowledge partial support from the Department of Energy (DOE ...
A room temperature halide exchange mediated cation exchange strategy leads to Ln3+ doping in pero... more A room temperature halide exchange mediated cation exchange strategy leads to Ln3+ doping in perovskite NPs.
We use kinetic modeling to explore the current-voltage, power-voltage, and power conversion effic... more We use kinetic modeling to explore the current-voltage, power-voltage, and power conversion efficiency characteristics of quantum dot dyads and triads as possible light absorption and charge separation engines in quantum dot, bulk heterojunction solar cells. The external and internal power conversion quantum efficiencies are significantly enhanced by introducing a third quantum dot between the donor and acceptor quantum dots. Given the constraint of comparable charge-recombination and charge-separation rates, open-circuit voltages for triads are predicted to be about 10%-17% larger than those for dyads, and short-circuit currents for triads are about 400% larger than those for dyads. These improvements in the efficiencies can be further enhanced by tuning the band-edge energy offset of the middle-position quantum dot from its neighbors. The band-edge energies of the middle quantum dot should be tuned so that they form a cascading band-edge energy alignment from the band-edge energies of the left CdTe QD to the
We investigate a spin-boson inspired model of electron transfer, where the diabatic coupling is g... more We investigate a spin-boson inspired model of electron transfer, where the diabatic coupling is given by a position-dependent phase, e iW x. We consider both equilibrium and nonequilibrium initial conditions. We show that, for this model, all equilibrium results are completely invariant to the sign of W (to infinite order). However, the nonequilibrium results do depend on the sign of W , suggesting that photo-induced electron transfer dynamics are meaningfully affected by Berry forces even in the presence of nuclear friction; furthermore, whenever there is spin-orbit coupling, electronic spin polarization can emerge (at least for some time).
The chiro-optical properties of CsPbBr3 nanoparticles (NP) capped by chiral organic ligands are s... more The chiro-optical properties of CsPbBr3 nanoparticles (NP) capped by chiral organic ligands are strongly dependent on their size, with the CD response of the first exciton band decreasing 100-fold upon tripling the NP edge length.
Cu-Ni castings and wrought pipes nominally contain 1% Fe to 2% Fe, which is added to improve the ... more Cu-Ni castings and wrought pipes nominally contain 1% Fe to 2% Fe, which is added to improve the Cu-Ni alloy's erosioncorrosion resistance. After fabrication, Cu-Ni products are solution heat-treated to dissolve the iron uniformly andform a single-phase alloy. During welding, however, iron can precipitatefrom solid solution onto grain boundaries in the heat-alfected zones (HAZ). During seawater service, these iron-rich precipitates can dissolve preferentially (galvanically), leading to intergranular corrosion of the HAZ. The present report described 90-10 Cu-Ni alloys in which different soluble elements were substitutedfor iron. Jetimpingement testing in filtered natural seawater showed that 2% In also promoted improved erosion-eorrosion resistance. Because indium is very soluble in copper, it should not precipitate in the HAZ dUring welding and cause intergranular corrosion of the HAZ dUring seawater service. The present study reviewed the literature on the mechanisms by which iron is believed to improve the erosion-eorrosion resistance, and proposed a different model based on doping of the thin surface oxidefzlm.
The recent convergence of chiral molecules with metal halide perovskite frameworks gives rise to ... more The recent convergence of chiral molecules with metal halide perovskite frameworks gives rise to an interesting family of chiral systems: two-dimensional, chiral hybrid organic−inorganic perovskites (chiral-HOIPs). While possessing photovoltaic properties of traditional HOIPs, this class of materials is endowed with chirality through its organic ligands in which the degeneracy of the electron spin in charge transport is broken. That is, the chirality-induced spin selectivity (CISS) effect manifests, making it a promising platform to bridge optospintronic studies and the CISS effect. In this work, chiral-HOIP/NiFe heterostructures are studied by means of the magneto-optical Kerr effect using a Sagnac interferometer. Upon illumination of the chiral-HOIPs, the Kerr signal at the chiral-HOIP/NiFe interface changes, and a linear dependence of the response on the magnetic field is observed. The sign of the slope was found to depend on the chirality of the HOIPs. The results demonstrate the utility of chiral-HOIP materials for chiral opto-spintronic applications.
Different conformers for meta-methylstilbenes cause nonexponential decay of the trans excited sta... more Different conformers for meta-methylstilbenes cause nonexponential decay of the trans excited state. The decay kinetics of these molecules is used to explore the nature of the reaction coordinate.
Experimental studies of the time-resolved bangap emission of CdSe are used to probe the attribute... more Experimental studies of the time-resolved bangap emission of CdSe are used to probe the attributes required in a theoretical model for the carrier dynamics of semiconductor electrodes. By variation of excitation conditions and material properties, the validity of approximations in a commonly used model are tested. The experimental results show that the details of bulk recombination, the effects of self-absorption, and the influence of the space charge field are quite important factors for the carrier dynamics. Simulation results show that the detailed kinetics of the interfacial recombination can also have important consequences for the carrier relaxation. Appropriate modeling of these processes is needed before a surface recombination velocity can be extracted from such studies in a quantitative manner. 43 refs., 9 figs., 2 tabs.
Optical transmission through subwavelength nanoaperture arrays can be modulated by metallic nanop... more Optical transmission through subwavelength nanoaperture arrays can be modulated by metallic nanoparticles that are nested in the nanoaperture. The localized surface plasmon resonance of nanoparticles can strongly modulate and in some cases dominate the transmission.
The rate of photoisomerization of 4,4‐dimethoxystilbene has been studied in two solvent series. T... more The rate of photoisomerization of 4,4‐dimethoxystilbene has been studied in two solvent series. These studies reveal that a separation of solvent and intramolecular effects is possible in the n‐alkanes, but not the n‐alcohols. The experimental results are interpreted in terms of the dynamical solvent response.
Journal of Physical Chemistry Letters, Oct 11, 2018
photoluminescence in doped tin dioxide [Sn(Ln)O 2 ] and doped titanium dioxide [Ti(Ln)O 2 ] nanop... more photoluminescence in doped tin dioxide [Sn(Ln)O 2 ] and doped titanium dioxide [Ti(Ln)O 2 ] nanoparticles shows that the emission efficiency of trivalent lanthanide cations (Ln 3+) in an oxide matrix can be improved by change of the cation site symmetry. An analysis of Ln 3+ emission quantum yield and asymmetry ratio is used to identify the importance of symmetry breaking around the dopant site for enhancing the Ln 3+ emission intensity. These findings identify an important criterion for engineering the luminescence intensity of dopant ions in semiconductor nanoparticle-based luminophores, which goes beyond the primary criterion of engineering the relative positions of the dopant energy levels with respect to the band edges of the host nanoparticle matrix.
... recommend 5.3 mg/m3 as the 15-min exposure limit.25 However, the hexadecanethiol SAM on a car... more ... recommend 5.3 mg/m3 as the 15-min exposure limit.25 However, the hexadecanethiol SAM on a carefully rinsed sur-face was in ... This work was funded by Liz Claiborne Accesso-ries, Inc., and Waldeck and Gu acknowledge partial support from the Department of Energy (DOE ...
A room temperature halide exchange mediated cation exchange strategy leads to Ln3+ doping in pero... more A room temperature halide exchange mediated cation exchange strategy leads to Ln3+ doping in perovskite NPs.
We use kinetic modeling to explore the current-voltage, power-voltage, and power conversion effic... more We use kinetic modeling to explore the current-voltage, power-voltage, and power conversion efficiency characteristics of quantum dot dyads and triads as possible light absorption and charge separation engines in quantum dot, bulk heterojunction solar cells. The external and internal power conversion quantum efficiencies are significantly enhanced by introducing a third quantum dot between the donor and acceptor quantum dots. Given the constraint of comparable charge-recombination and charge-separation rates, open-circuit voltages for triads are predicted to be about 10%-17% larger than those for dyads, and short-circuit currents for triads are about 400% larger than those for dyads. These improvements in the efficiencies can be further enhanced by tuning the band-edge energy offset of the middle-position quantum dot from its neighbors. The band-edge energies of the middle quantum dot should be tuned so that they form a cascading band-edge energy alignment from the band-edge energies of the left CdTe QD to the
We investigate a spin-boson inspired model of electron transfer, where the diabatic coupling is g... more We investigate a spin-boson inspired model of electron transfer, where the diabatic coupling is given by a position-dependent phase, e iW x. We consider both equilibrium and nonequilibrium initial conditions. We show that, for this model, all equilibrium results are completely invariant to the sign of W (to infinite order). However, the nonequilibrium results do depend on the sign of W , suggesting that photo-induced electron transfer dynamics are meaningfully affected by Berry forces even in the presence of nuclear friction; furthermore, whenever there is spin-orbit coupling, electronic spin polarization can emerge (at least for some time).
The chiro-optical properties of CsPbBr3 nanoparticles (NP) capped by chiral organic ligands are s... more The chiro-optical properties of CsPbBr3 nanoparticles (NP) capped by chiral organic ligands are strongly dependent on their size, with the CD response of the first exciton band decreasing 100-fold upon tripling the NP edge length.
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Papers by David Waldeck