James Heflin | Virginia Tech (original) (raw)

Papers by James Heflin

Research paper thumbnail of Organic Optoelectronic Nanostructures

Nanostructure Science and Technology, 2004

Research paper thumbnail of Fiber-optic sensor or modulator using tuning of long period gratings with self-assembled layers

The provision of an ionic self-assembled multilayer (ISAM) film on a fiber-optic element includin... more The provision of an ionic self-assembled multilayer (ISAM) film on a fiber-optic element including a long period grating (LPG) by a simple, room temperature process provides tuning of the LPG and/or high sensitivity to the refractive index of the ambient environment of the fiber-optic element. Inclusion of a final layer or a probe, receptor or affinity ligand in the multi-layer film provides a highly sensitive sensor for specific chemical and biological materials. Use of a turn around point (TAP) LPG allows detection to be performed by ...

Research paper thumbnail of Introduction to Nanoscale Science and Technology

Research paper thumbnail of Microscopic origin of third-order properties of rigid rod polymer structures (A)

Title: Microscopic origin of third-order properties of rigid rod polymer structures (A). Authors:... more Title: Microscopic origin of third-order properties of rigid rod polymer structures (A). Authors: Heflin, JR; Wong, King-Young; Zamani-Khamiri, O.; Garito, AF; Bitler, SP; Wolfe, JF. Publication: J. Opt. Soc. Am. B, vol. 4, page P136. Publication Date: 02/1987. Origin: OSA. ...

Research paper thumbnail of Electron Correlation Theory and Experimental Measurements of the Third-Order Nonlinear Optical Properties of Conjugated Linear Chains

Comprehensive theoretical and experimental studies of the magnitude, sign, dispersion, and length... more Comprehensive theoretical and experimental studies of the magnitude, sign, dispersion, and length dependence of the third order molecular susceptibility gamma _{ijkl}(-omega_4 ;omega_1, omega_2, omega_3 ) demonstrate that the microscopic origin of the nonresonant third order nonlinear optical properties of conjugated linear chains is determined by the effects of electron correlation due to electron-electron repulsion. Multiple -excited configuration interaction calculations of

Research paper thumbnail of Excited-state enhancement of nonresonant degenerate four-wave mixing In conjugated linear chains

Research paper thumbnail of Sensitive optical response of long period fiber gratings to nm-thick ionic self-assembled multilayers

Abstract Ionic-self-assembled-multilayers of nm-thicknesses are deposited on long period gratings... more Abstract Ionic-self-assembled-multilayers of nm-thicknesses are deposited on long period gratings. We observe dramatic resonant-wavelength shifts even with nm-thick films. We demonstrate feasibility of this highly controllable deposition-technique for fine-tuning grating properties, and for use as biosensors.

Research paper thumbnail of Advances in Polymer-Fullerene Photovoltaic Devices

Research paper thumbnail of i Sensitivity control of optical fiber biosensors utilizing turnaround point long period gratings with self-assembled polymer coatings

Biosensors have a multitude of important applications in basic research, environmental monitoring... more Biosensors have a multitude of important applications in basic research, environmental monitoring, biodefense, and medicine. This research aims to show that Ionic Self-Assembled Multilayers (ISAMs) adsorbed on Long Period Gratings (LPGs) can serve as a highly sensitive, robust, inexpensive optical-based biosensor platform.

Research paper thumbnail of Nonlinear optical properties of linear chains and electron-correlation effects

Physical review. B, Condensed matter, Jan 15, 1988

The large third-order nonlinear optical properties γ ijkl (-ω 4 ;ω 1 ,ω 2 ,ω 3 ) observed for con... more The large third-order nonlinear optical properties γ ijkl (-ω 4 ;ω 1 ,ω 2 ,ω 3 ) observed for conjugated organic linear chains, such as polyenes, are explained by strong electron-correlation behavior in virtual, two-photon 1 A g states. The dominant chain axis component γ xxxx is found to ...

Research paper thumbnail of Excited-state enhancement of third-order nonlinear optical responses in conjugated organic chains

Physical review. A, 1995

We present the details of an experimental observation of excited-state enhancement of the degener... more We present the details of an experimental observation of excited-state enhancement of the degenerate-four-wave-mixing (DFWM) susceptibility gammaSn(-omegaomega,omega,-omega) of a conjugated linear chain, diphenylexatriene (DPH), when the first pi-electron excited state is populated for nanosecond time scales and then probed nonresonantly through picosecond DFWM. An increase as large as a factor of 100 in the completely nonresonant 1064-nm DFWM signal from

Research paper thumbnail of Nonlinear Optical Properties of Polyenes: Electron Correlation and Chain Conformation

Research paper thumbnail of Invited Paper Recent Developments In Microscopic Descriptions Of The Nonlinear Optical Properties Of Organic And Polymer Structures

Research paper thumbnail of Symmetry-controlled electron correlation mechanism for third order nonlinear optical properties of conjugated linear chains

Research paper thumbnail of Recent studies on the nonlinear optical properties of conjugated linear chains and rigid rod polymers

Research paper thumbnail of Active Photonic Crystal Devices in Self-Assembled Electro-Optic Polymeric Materials

MRS Proceedings, 2004

Photonic crystals (PC) offer novel and potent approaches for the control of light compared to tra... more Photonic crystals (PC) offer novel and potent approaches for the control of light compared to traditional technologies. The development of a photonic crystal technology in electro-optic (EO) materials would now provide a novel approach for the development and integration of important "active devices" such as switch, interferometers, etc. We report the development of an active photonic crystal technology that uses

Research paper thumbnail of Analysis of optical response of long period fiber gratings to nm-thick thin-film coating

Optics Express, 2005

We have theoretically and experimentally demonstrated that the resonant wavelength of long period... more We have theoretically and experimentally demonstrated that the resonant wavelength of long period fiber gratings (LPG) can be shifted by a large magnitude by coating with only a nm-thick thin-film that has a refractive index higher than that of the glass cladding. The resonant wavelength shift can result from either the variation of the thickness of the film and/or the variation of its refractive index. These results demonstrate the sensitivity of LPG-based sensors can be enhanced by using a film of nm-thickness and refractive index greater than silica. This coating schematic offers an efficient platform for achieving high-performance indexmodulating fiber devices and high-performance index/thickness-sensing LPG-based fiber sensors for detecting optical property variations of the thinfilm coating.

Research paper thumbnail of Biosensors employing ionic self-assembled multilayers adsorbed on long-period fiber gratings

Sensors and Actuators B: Chemical, 2009

We demonstrate that ionic self-assembled multilayers (ISAMs) adsorbed on long period gratings (LP... more We demonstrate that ionic self-assembled multilayers (ISAMs) adsorbed on long period gratings (LPGs) function effectively as biosensors using biotin-streptavidin as a demonstration bioconjugate pair. Biotin, streptavidin, and anti-streptavidin were deposited onto the ISAM-coated LPG sequentially, each inducing a measurable resonant wavelength shift of the LPG. Control experiments verified the specificity of the biosensor system. Furthermore, we demonstrate that ISAM coated turnaround point LPGs could serve as highly sensitive biosensors that exhibit a change in transmitted intensity rather than resonant wavelength. Experimental measurements confirm that ISAM-coated LPGs provide an attractive platform for building efficient and high-performance optical sensors.

Research paper thumbnail of Optics beyond the limits

Research paper thumbnail of Fabrication and characterization of ZnTPP:PCBM bulk heterojunction (BHJ) solar cells

Journal of Physics and Chemistry of Solids, 2011

Bulk heterojunction (BHJ) solar cells were fabricated based on blended films of a porphyrin deriv... more Bulk heterojunction (BHJ) solar cells were fabricated based on blended films of a porphyrin derivative 5,10,15,20-Tetraphenyl-21H,23H-porphine zinc (ZnTPP) and a fullerene derivative [6,6]-phenyl-C 61 butyric acid methyl ester (PCBM) as the active layer. The ZnTTP:PCBM BHJ solar cells were fabricated by spin-casting of the blended layer. The weight ratios of ZnTPP and PCBM were varied from 1:1 to 0:10. The electronic and optical properties of each cell were investigated. Optical density (OD) of the blended film for each cell was extracted from its reflection and transmission curves. OD and average absorption coefficients of the active materials were used to determine film thicknesses. Absorption spectra of each component material were compared with the spectra of the blended films. Current density-Voltage (J-V) characteristics were recorded under dark as well as under the illumination of AM 1.5G (1 sun) solar spectrum. The BHJ solar cell with ZnTPP:PCBM ratio of 1:9 showed the best performance . The values of RR, V OC , J SC , FF and Z for these ratios were 106.3, 0.4 V, 1.316 mA/cm 2 , 0.4 and 0.21%, respectively. The cross-section of this device using SEM was also examined.

Research paper thumbnail of Organic Optoelectronic Nanostructures

Nanostructure Science and Technology, 2004

Research paper thumbnail of Fiber-optic sensor or modulator using tuning of long period gratings with self-assembled layers

The provision of an ionic self-assembled multilayer (ISAM) film on a fiber-optic element includin... more The provision of an ionic self-assembled multilayer (ISAM) film on a fiber-optic element including a long period grating (LPG) by a simple, room temperature process provides tuning of the LPG and/or high sensitivity to the refractive index of the ambient environment of the fiber-optic element. Inclusion of a final layer or a probe, receptor or affinity ligand in the multi-layer film provides a highly sensitive sensor for specific chemical and biological materials. Use of a turn around point (TAP) LPG allows detection to be performed by ...

Research paper thumbnail of Introduction to Nanoscale Science and Technology

Research paper thumbnail of Microscopic origin of third-order properties of rigid rod polymer structures (A)

Title: Microscopic origin of third-order properties of rigid rod polymer structures (A). Authors:... more Title: Microscopic origin of third-order properties of rigid rod polymer structures (A). Authors: Heflin, JR; Wong, King-Young; Zamani-Khamiri, O.; Garito, AF; Bitler, SP; Wolfe, JF. Publication: J. Opt. Soc. Am. B, vol. 4, page P136. Publication Date: 02/1987. Origin: OSA. ...

Research paper thumbnail of Electron Correlation Theory and Experimental Measurements of the Third-Order Nonlinear Optical Properties of Conjugated Linear Chains

Comprehensive theoretical and experimental studies of the magnitude, sign, dispersion, and length... more Comprehensive theoretical and experimental studies of the magnitude, sign, dispersion, and length dependence of the third order molecular susceptibility gamma _{ijkl}(-omega_4 ;omega_1, omega_2, omega_3 ) demonstrate that the microscopic origin of the nonresonant third order nonlinear optical properties of conjugated linear chains is determined by the effects of electron correlation due to electron-electron repulsion. Multiple -excited configuration interaction calculations of

Research paper thumbnail of Excited-state enhancement of nonresonant degenerate four-wave mixing In conjugated linear chains

Research paper thumbnail of Sensitive optical response of long period fiber gratings to nm-thick ionic self-assembled multilayers

Abstract Ionic-self-assembled-multilayers of nm-thicknesses are deposited on long period gratings... more Abstract Ionic-self-assembled-multilayers of nm-thicknesses are deposited on long period gratings. We observe dramatic resonant-wavelength shifts even with nm-thick films. We demonstrate feasibility of this highly controllable deposition-technique for fine-tuning grating properties, and for use as biosensors.

Research paper thumbnail of Advances in Polymer-Fullerene Photovoltaic Devices

Research paper thumbnail of i Sensitivity control of optical fiber biosensors utilizing turnaround point long period gratings with self-assembled polymer coatings

Biosensors have a multitude of important applications in basic research, environmental monitoring... more Biosensors have a multitude of important applications in basic research, environmental monitoring, biodefense, and medicine. This research aims to show that Ionic Self-Assembled Multilayers (ISAMs) adsorbed on Long Period Gratings (LPGs) can serve as a highly sensitive, robust, inexpensive optical-based biosensor platform.

Research paper thumbnail of Nonlinear optical properties of linear chains and electron-correlation effects

Physical review. B, Condensed matter, Jan 15, 1988

The large third-order nonlinear optical properties γ ijkl (-ω 4 ;ω 1 ,ω 2 ,ω 3 ) observed for con... more The large third-order nonlinear optical properties γ ijkl (-ω 4 ;ω 1 ,ω 2 ,ω 3 ) observed for conjugated organic linear chains, such as polyenes, are explained by strong electron-correlation behavior in virtual, two-photon 1 A g states. The dominant chain axis component γ xxxx is found to ...

Research paper thumbnail of Excited-state enhancement of third-order nonlinear optical responses in conjugated organic chains

Physical review. A, 1995

We present the details of an experimental observation of excited-state enhancement of the degener... more We present the details of an experimental observation of excited-state enhancement of the degenerate-four-wave-mixing (DFWM) susceptibility gammaSn(-omegaomega,omega,-omega) of a conjugated linear chain, diphenylexatriene (DPH), when the first pi-electron excited state is populated for nanosecond time scales and then probed nonresonantly through picosecond DFWM. An increase as large as a factor of 100 in the completely nonresonant 1064-nm DFWM signal from

Research paper thumbnail of Nonlinear Optical Properties of Polyenes: Electron Correlation and Chain Conformation

Research paper thumbnail of Invited Paper Recent Developments In Microscopic Descriptions Of The Nonlinear Optical Properties Of Organic And Polymer Structures

Research paper thumbnail of Symmetry-controlled electron correlation mechanism for third order nonlinear optical properties of conjugated linear chains

Research paper thumbnail of Recent studies on the nonlinear optical properties of conjugated linear chains and rigid rod polymers

Research paper thumbnail of Active Photonic Crystal Devices in Self-Assembled Electro-Optic Polymeric Materials

MRS Proceedings, 2004

Photonic crystals (PC) offer novel and potent approaches for the control of light compared to tra... more Photonic crystals (PC) offer novel and potent approaches for the control of light compared to traditional technologies. The development of a photonic crystal technology in electro-optic (EO) materials would now provide a novel approach for the development and integration of important "active devices" such as switch, interferometers, etc. We report the development of an active photonic crystal technology that uses

Research paper thumbnail of Analysis of optical response of long period fiber gratings to nm-thick thin-film coating

Optics Express, 2005

We have theoretically and experimentally demonstrated that the resonant wavelength of long period... more We have theoretically and experimentally demonstrated that the resonant wavelength of long period fiber gratings (LPG) can be shifted by a large magnitude by coating with only a nm-thick thin-film that has a refractive index higher than that of the glass cladding. The resonant wavelength shift can result from either the variation of the thickness of the film and/or the variation of its refractive index. These results demonstrate the sensitivity of LPG-based sensors can be enhanced by using a film of nm-thickness and refractive index greater than silica. This coating schematic offers an efficient platform for achieving high-performance indexmodulating fiber devices and high-performance index/thickness-sensing LPG-based fiber sensors for detecting optical property variations of the thinfilm coating.

Research paper thumbnail of Biosensors employing ionic self-assembled multilayers adsorbed on long-period fiber gratings

Sensors and Actuators B: Chemical, 2009

We demonstrate that ionic self-assembled multilayers (ISAMs) adsorbed on long period gratings (LP... more We demonstrate that ionic self-assembled multilayers (ISAMs) adsorbed on long period gratings (LPGs) function effectively as biosensors using biotin-streptavidin as a demonstration bioconjugate pair. Biotin, streptavidin, and anti-streptavidin were deposited onto the ISAM-coated LPG sequentially, each inducing a measurable resonant wavelength shift of the LPG. Control experiments verified the specificity of the biosensor system. Furthermore, we demonstrate that ISAM coated turnaround point LPGs could serve as highly sensitive biosensors that exhibit a change in transmitted intensity rather than resonant wavelength. Experimental measurements confirm that ISAM-coated LPGs provide an attractive platform for building efficient and high-performance optical sensors.

Research paper thumbnail of Optics beyond the limits

Research paper thumbnail of Fabrication and characterization of ZnTPP:PCBM bulk heterojunction (BHJ) solar cells

Journal of Physics and Chemistry of Solids, 2011

Bulk heterojunction (BHJ) solar cells were fabricated based on blended films of a porphyrin deriv... more Bulk heterojunction (BHJ) solar cells were fabricated based on blended films of a porphyrin derivative 5,10,15,20-Tetraphenyl-21H,23H-porphine zinc (ZnTPP) and a fullerene derivative [6,6]-phenyl-C 61 butyric acid methyl ester (PCBM) as the active layer. The ZnTTP:PCBM BHJ solar cells were fabricated by spin-casting of the blended layer. The weight ratios of ZnTPP and PCBM were varied from 1:1 to 0:10. The electronic and optical properties of each cell were investigated. Optical density (OD) of the blended film for each cell was extracted from its reflection and transmission curves. OD and average absorption coefficients of the active materials were used to determine film thicknesses. Absorption spectra of each component material were compared with the spectra of the blended films. Current density-Voltage (J-V) characteristics were recorded under dark as well as under the illumination of AM 1.5G (1 sun) solar spectrum. The BHJ solar cell with ZnTPP:PCBM ratio of 1:9 showed the best performance . The values of RR, V OC , J SC , FF and Z for these ratios were 106.3, 0.4 V, 1.316 mA/cm 2 , 0.4 and 0.21%, respectively. The cross-section of this device using SEM was also examined.