ABSTRACT Many implantable biomedical devices suffer from post-operative infections. To effectivel... more ABSTRACT Many implantable biomedical devices suffer from post-operative infections. To effectively treat post-operative infections, prevention of biofilm and tissue integrations needs to be addressed simultaneously. In this manuscript, we report the direct laser patterning of SAMs on Co-Cr alloy that could serve as a platform for multi-therapeutic delivery. A sapphire femtosecond pulsed laser was used to etch the SAMs on the Co-Cr alloy. Atomic force microscope (AFM) showed the surface topography before and after the laser etches as well as determined the diameter of laser etches. The experimental value of the diameter of the laser etch closely matched the theoretical predicted values.
We present low-temperature photoluminescence spectra of molecular-beam epitaxy (MBE) and organo-m... more We present low-temperature photoluminescence spectra of molecular-beam epitaxy (MBE) and organo-metallic vapor-phase epitaxy (OMVPE) ZnTe layers deposited on GaAs substrates under different growth conditions. Strong bands associated with Zn vacancies are observed in the MBE materials, while the OMVPE spectra are dominated by sharp impurity-related lines. A number of instrinsic and extrinsic emission lines are identified. No significant shift of these lines is observed relative to their positions in bulk ZnTe, implying stress levels less than 0.1 kbar for both the MBE and OMVPE layers. A study of the effects of the Zn:Te ratio in the MBE growth chamber reveals that for a growth temperature of 325 °C, an optimal value of ∼2.2 produces the highest photoluminescence efficiencies and the strongest intrinsic features. The relative intensity of the vacancy-related emission decreases as the Zn:Te ratio is increased.
abstract The behavior of spontaneous emission of emitters embedded inside metamaterials with hype... more abstract The behavior of spontaneous emission of emitters embedded inside metamaterials with hyperbolic dispersion has been investigated. A simple technique has been developed to fabricate lamellar metal-dielectric hyperbolic metamaterials on substrates which can be flat, flexible or curvilinear in geometry. Moreover, this method opens up the possibility of functionalizing the dielectric layers by dye molecules. Utilizing this technique, we study the spontaneous emission kinetics of emitters placed either on top, or embedded inside ...
ABSTRACT A comparison study between a block copolymer and blend samples (D/A; donor/acceptor) rev... more ABSTRACT A comparison study between a block copolymer and blend samples (D/A; donor/acceptor) revealed that their optoelectronic properties change significantly in different morphologies due to different processing conditions. The study shows that the photovoltaic performance of a block copolymer is better than that of corresponding donor/acceptor simple blend devices due to smaller scale (5-10 nanometers) donor/acceptor phase separation in the block copolymer, and that thermal annealing generally improves OE property due to potential better molecular packing.
Optimizations of organic/polymeric optoelectronic materials and devices in both space and energy/... more Optimizations of organic/polymeric optoelectronic materials and devices in both space and energy/time domains have been studied, both experimentally and theoretically, in order to achieve high efficiency photoelectric conversion. Specifically, at spatial domain, a 'tertiary' block copolymer supra-molecular nano structure has been designed, and a series of -DBAB- type of block copolymers, where D is a conjugated donor block, A is a conjugated acceptor block, and B is a non-conjugated and flexible bridge unit, have been synthesized, characterized, and preliminarily examined for photoelectric conversions. In comparison to simple donor/acceptor (D/A) blends, -DBAB- block copolymers exhibited much better photoluminescence quenching and photoconductivity. These are mainly attributed to improvement in spatial domain for charge carrier generation and transportation in -DBAB- block copolymers then in simple D/A blends. In materials energy levels and electron transfer dynamic regime, theoretical analysis revealed that, the photo (or thermal) excitation induced charge separation appears to be most efficient when the corresponding donor/acceptor frontier orbital level offset is equal to the sum of the charge separation reorganization energy and the exciton binding energy. Other donor/acceptor frontier orbital energy offsets were also identified where the charge recombination becomes most severe, and where the charge separation rate constant over charge recombination rate constant become largest. This dynamically favored charge separation mechanism is also proposed to explain the general 'doping' induced charge carrier generation. Implications of these findings and future approaches are also discussed in order to achieve inexpensive, lightweight, flexible, and high efficiency 'plastic' solar cells or photo detectors.
In EO polymer materials, the second-order nonlinear optic chromophores must be oriented in one di... more In EO polymer materials, the second-order nonlinear optic chromophores must be oriented in one direction in order to be electro-optically active. Interchromophore electrostatic interactions, which encourages the formation of non-active and light-scattering crystalline ...
We have investigated the temperatdre dependence of the photoluminescence (PL) decay kinetics of a... more We have investigated the temperatdre dependence of the photoluminescence (PL) decay kinetics of a series of GaAs/AlAs quantum well structures where the GaAs thickness was kept constant at 25Å and the AlAs was varied between 41Å and 19Å. In these structures the band alignment is type II and the dominant photoluminescence process at 4K is due to recombination of excitons involving electrons confined at the AlAs X point and holes in the GaAs. At 4K on the low energy side of the zero phonon type II transition the PL decay is a single exponential over at least two decades. The time constant of this decay is a strong function of the AlAs layer thickness. The variation of this decay time is in line with a change in oscillation strength of the type II process due to the change in the mixing between the Xz(AlAs) electron states and the Γ (GaAs) electron states. At higher temperatures (T>15K) the photoluminescence intensity and the decay time decrease very rapidly with increasing temperature. This is due to the increased influence of non-radiative proceses as the type II excitons become delocalised.
Recent development of crosslinked NLO polymers for large bandwidth electro-optical modulations. [... more Recent development of crosslinked NLO polymers for large bandwidth electro-optical modulations. [Proceedings of SPIE 4580, 297 (2001)]. Sam-Shajing Sun, Shahin Maaref, Enver Alam, Yiqing Wang, Zhen Fan, Messaoud Bahoura, Patrick T. Higgins, Carl E. Bonner, Jr. ...
ABSTRACT Many implantable biomedical devices suffer from post-operative infections. To effectivel... more ABSTRACT Many implantable biomedical devices suffer from post-operative infections. To effectively treat post-operative infections, prevention of biofilm and tissue integrations needs to be addressed simultaneously. In this manuscript, we report the direct laser patterning of SAMs on Co-Cr alloy that could serve as a platform for multi-therapeutic delivery. A sapphire femtosecond pulsed laser was used to etch the SAMs on the Co-Cr alloy. Atomic force microscope (AFM) showed the surface topography before and after the laser etches as well as determined the diameter of laser etches. The experimental value of the diameter of the laser etch closely matched the theoretical predicted values.
We present low-temperature photoluminescence spectra of molecular-beam epitaxy (MBE) and organo-m... more We present low-temperature photoluminescence spectra of molecular-beam epitaxy (MBE) and organo-metallic vapor-phase epitaxy (OMVPE) ZnTe layers deposited on GaAs substrates under different growth conditions. Strong bands associated with Zn vacancies are observed in the MBE materials, while the OMVPE spectra are dominated by sharp impurity-related lines. A number of instrinsic and extrinsic emission lines are identified. No significant shift of these lines is observed relative to their positions in bulk ZnTe, implying stress levels less than 0.1 kbar for both the MBE and OMVPE layers. A study of the effects of the Zn:Te ratio in the MBE growth chamber reveals that for a growth temperature of 325 °C, an optimal value of ∼2.2 produces the highest photoluminescence efficiencies and the strongest intrinsic features. The relative intensity of the vacancy-related emission decreases as the Zn:Te ratio is increased.
abstract The behavior of spontaneous emission of emitters embedded inside metamaterials with hype... more abstract The behavior of spontaneous emission of emitters embedded inside metamaterials with hyperbolic dispersion has been investigated. A simple technique has been developed to fabricate lamellar metal-dielectric hyperbolic metamaterials on substrates which can be flat, flexible or curvilinear in geometry. Moreover, this method opens up the possibility of functionalizing the dielectric layers by dye molecules. Utilizing this technique, we study the spontaneous emission kinetics of emitters placed either on top, or embedded inside ...
ABSTRACT A comparison study between a block copolymer and blend samples (D/A; donor/acceptor) rev... more ABSTRACT A comparison study between a block copolymer and blend samples (D/A; donor/acceptor) revealed that their optoelectronic properties change significantly in different morphologies due to different processing conditions. The study shows that the photovoltaic performance of a block copolymer is better than that of corresponding donor/acceptor simple blend devices due to smaller scale (5-10 nanometers) donor/acceptor phase separation in the block copolymer, and that thermal annealing generally improves OE property due to potential better molecular packing.
Optimizations of organic/polymeric optoelectronic materials and devices in both space and energy/... more Optimizations of organic/polymeric optoelectronic materials and devices in both space and energy/time domains have been studied, both experimentally and theoretically, in order to achieve high efficiency photoelectric conversion. Specifically, at spatial domain, a 'tertiary' block copolymer supra-molecular nano structure has been designed, and a series of -DBAB- type of block copolymers, where D is a conjugated donor block, A is a conjugated acceptor block, and B is a non-conjugated and flexible bridge unit, have been synthesized, characterized, and preliminarily examined for photoelectric conversions. In comparison to simple donor/acceptor (D/A) blends, -DBAB- block copolymers exhibited much better photoluminescence quenching and photoconductivity. These are mainly attributed to improvement in spatial domain for charge carrier generation and transportation in -DBAB- block copolymers then in simple D/A blends. In materials energy levels and electron transfer dynamic regime, theoretical analysis revealed that, the photo (or thermal) excitation induced charge separation appears to be most efficient when the corresponding donor/acceptor frontier orbital level offset is equal to the sum of the charge separation reorganization energy and the exciton binding energy. Other donor/acceptor frontier orbital energy offsets were also identified where the charge recombination becomes most severe, and where the charge separation rate constant over charge recombination rate constant become largest. This dynamically favored charge separation mechanism is also proposed to explain the general 'doping' induced charge carrier generation. Implications of these findings and future approaches are also discussed in order to achieve inexpensive, lightweight, flexible, and high efficiency 'plastic' solar cells or photo detectors.
In EO polymer materials, the second-order nonlinear optic chromophores must be oriented in one di... more In EO polymer materials, the second-order nonlinear optic chromophores must be oriented in one direction in order to be electro-optically active. Interchromophore electrostatic interactions, which encourages the formation of non-active and light-scattering crystalline ...
We have investigated the temperatdre dependence of the photoluminescence (PL) decay kinetics of a... more We have investigated the temperatdre dependence of the photoluminescence (PL) decay kinetics of a series of GaAs/AlAs quantum well structures where the GaAs thickness was kept constant at 25Å and the AlAs was varied between 41Å and 19Å. In these structures the band alignment is type II and the dominant photoluminescence process at 4K is due to recombination of excitons involving electrons confined at the AlAs X point and holes in the GaAs. At 4K on the low energy side of the zero phonon type II transition the PL decay is a single exponential over at least two decades. The time constant of this decay is a strong function of the AlAs layer thickness. The variation of this decay time is in line with a change in oscillation strength of the type II process due to the change in the mixing between the Xz(AlAs) electron states and the Γ (GaAs) electron states. At higher temperatures (T>15K) the photoluminescence intensity and the decay time decrease very rapidly with increasing temperature. This is due to the increased influence of non-radiative proceses as the type II excitons become delocalised.
Recent development of crosslinked NLO polymers for large bandwidth electro-optical modulations. [... more Recent development of crosslinked NLO polymers for large bandwidth electro-optical modulations. [Proceedings of SPIE 4580, 297 (2001)]. Sam-Shajing Sun, Shahin Maaref, Enver Alam, Yiqing Wang, Zhen Fan, Messaoud Bahoura, Patrick T. Higgins, Carl E. Bonner, Jr. ...
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