Ryan Ries | California Institute of Technology (original) (raw)

Papers by Ryan Ries

The Journal of Physical Chemistry B, 2002

The chemical interactions between single walled carbon nanotubes (SWNTs) and two structurally sim... more The chemical interactions between single walled carbon nanotubes (SWNTs) and two structurally similar polymers, poly{(m-phenylenevinylene)-co-[(2,5-dioctyloxy-p-phenylene)vinylene]}, or PmPV, and poly{(2,6pyridinylenevinylene)-co-[(2,5-dioctyloxy-p-phenylene)vinylene]}, or PPyPV, are investigated. The fundamental difference between these two polymers is that PPyPV is a base and is readily protonated via the addition of HCl. Both polymers promote chloroform solubilization of SWNTs. We find that the SWNT/PPyPV interaction lowers the pK a of PPyPV. Optoelectronic devices, fabricated from single polymer-wrapped SWNT structures, reveal a photogating effect on charge transport which can rectify or amplify current flow through the tubes. For PmPV wrapped tubes, the wavelength dependence of this effect correlates to the absorption spectrum of PmPV. For PPyPV, the wavelength dependence correlates with the absorption spectrum of protonated PPyPV, indicating that SWNTs assist in charge stabilization.

The Journal of Physical Chemistry B

... L. Sample, † Ryan Ries, Eileen M. Spain, and James R. Heath*. ... Prospects of Colloidal Nano... more ... L. Sample, † Ryan Ries, Eileen M. Spain, and James R. Heath*. ... Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications. Dmitri V. Talapin, Jong-Soo Lee, Maksym V. Kovalenko and Elena V. Shevchenko. Chemical Reviews 2010 110 (1), 389-458. ...

Langmuir, 2004

A method for the spatially selective biofunctionalization of silicon micro-and nanostructures is ... more A method for the spatially selective biofunctionalization of silicon micro-and nanostructures is reported, and results are presented for both single-crystal silicon (111) or (100) surfaces. An electroactive monolayer of hydroquinone was formed on the surface of H-terminated silicon working electrodes via an olefin reaction with UV-generated surface radicals. Molecules presenting either cyclopentadiene or a thiol group can be immobilized onto the regions where the hydroquinone has been oxidized. Molecular size and crystal orientation are evaluated as important factors that dictate the electrode stability in aqueous solution under anodic potentials. Monolayers composed of smaller molecules on (111) surfaces exhibit the highest packing density and are more effective in preventing anodic oxidation of the underlying substrate. Voltammetry, X-ray photoelectron spectroscopy, and atomic force and fluorescence microscopy are utilized to interrogate the kinetic rates of biofunctionalization, the extent of surface coverage, monolayer quality, and the spatial selectivity of the process.

Electrochimica Acta, 2006

A novel and sensitive electrochemical DNA biosensor based on electrochemically fabricated polyani... more A novel and sensitive electrochemical DNA biosensor based on electrochemically fabricated polyaniline nanowire and methylene blue for DNA hybridization detection is presented. Nanowires of conducting polymers were directly synthesized through a three-step electrochemical deposition procedure in an aniline-containing electrolyte solution, by using the glassy carbon electrode (GCE) as the working electrode. The morphology of the polyaniline films was examined using a field emission scanning electron microscope (SEM). The diameters of the nanowires range from 80 to 100 nm. The polyaniline nanowires-coated electrode exhibited very good electrochemical conductivity. Oligonucleotides with phosphate groups at the 5 end were covalently linked onto the amino groups of polyaniline nanowires on the electrode. The hybridization events were monitored with differential pulse voltammetry (DPV) measurement using methylene blue (MB) as an indicator. The approach described here can effectively discriminate complementary from non-complementary DNA sequence, with a detection limit of 1.0 × 10 −12 mol l −1 of complementary target, suggesting that the polyaniline nanowires hold great promises for sensitive electrochemical biosensor applications.

Chirality, 2002

The chiral recognition phenomenon observed in enantioselective excited-state energy transfer proc... more The chiral recognition phenomenon observed in enantioselective excited-state energy transfer processes currently requires the use of chiroptical spectroscopic techniques to probe the magnitude and sense of the discriminatory interactions. The use of chiroptical spectroscopic techniques limits the study of chiral recognition to those molecular species with strong absorption or emission dissymmetry factors. This study presents the theoretical and experimental methodology to determine the magnitude of chiral discriminatory interactions with unpolarized, steady-state luminescence measurements. Based on bimolecular luminescence quenching kinetics for a system containing chiral molecules, the Stern-Volmer equation is derived and contains a chiral discriminatory term for a system containing a chiral but racemic luminophore and an enantiomerically resolved quencher species. The utility of this methodology is confirmed by examining the enantioselective excited-state quenching between several Lndpa 3À 3 complexes (where Ln = Eu 3+ , Tb 3+ , or Dy 3+ and dpa = pyridine-2,6-dicarboxylate) acting as the energy donor and either racemic or enantiomerically resolved Codach 3 3 (where dach = trans-1R,2R (or 1S,2S)-diaminocyclohexane) acting as the energy acceptor in an aqueous solution. The results of this study confirm the utility of unpolarized, steady-state luminescence measurements as a probe of chiral discriminatory behavior. Chirality 14:456À464, 2002.

The Journal of Physical Chemistry B, 2004

The structure and long-time dynamics of suspended lipid bilayers made of 1-stearoyl-2-oleoyl-sn-g... more The structure and long-time dynamics of suspended lipid bilayers made of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (SOPE) in the gel phase was interrogated using electrical measurements co-recorded with second harmonic generation (SHG) micrographs. SHG microscopy was shown to be an efficient method for distinguishing between the regions of bilayer and annulus as well as probing structural and dynamical variations within a single bilayer. Micromachined silicon chips and two types of plastic partitions, delrin and polyethylene, were investigated as substrate materials. Silicon chips yielded the most stable bilayers, lasting for 1 or 2 days. The membrane characteristics, including the amount of incorporated solvent within the bilayer, the dynamics of bilayer formation, and the stability of the bilayer, were found to be strongly substratedependent. In a second set of experiments, SHG-active membrane dyes, di-8-ANEPPS and di-4-ANEPPS, were used to interrogate the domain structure of the same suspended bilayers using scanning two-photon fluorescence (2PF) and SHG microscopy, again correlated with capacitance measurements. Using these dyes, an enhancement in the SHG signal due to membrane potential was recorded, and the rates of molecular diffusion for di-4-ANEPPS through the membrane were investigated. Polarization-resolved SHG imaging was used to determine the orientation of the dye molecules within the membrane.

Low-temperature scanning tunneling microscopy (STM) has been used to image CH3-terminated Si(111)... more Low-temperature scanning tunneling microscopy (STM) has been used to image CH3-terminated Si(111) surfaces that were prepared through a chlorination/alkylation procedure. The STM data revealed a well-ordered structure commensurate with the atop sites of an unreconstructed 1 1 overlayer on the silicon (111) surface. Images collected at 4.7 K revealed bright spots, separated by 0.18 ( 0.01 nm, which are assigned to adjacent H atoms on the same methyl group. The C-H bonds in each methyl group were observed to be rotated by 7 ( 3 ° away from the center of an adjacent methyl group and toward an underlying Si atom. Hence, the predominant interaction that determines the surface structure arises from repulsions between hydrogen atoms on neighboring methyl groups, and secondary interactions unique to the surface are also evident. Hydrogen-terminated (111)-oriented Si surfaces are well documented to have a low number of structural and electrically active defect sites.1,2 However, these surfac...

Underwater imaging of the air environment is described with particular attention given to the opt... more Underwater imaging of the air environment is described with particular attention given to the optical problems of near-horizon viewing. These include severe chromatic aberration from transmission through the seawater wedge, the horizon distortion effect, ...

Bulletin of the American Physical Society, 2005

Submitted for the MAR05 Meeting of The American Physical Society STM Characterization of Si Surfa... more Submitted for the MAR05 Meeting of The American Physical Society STM Characterization of Si Surface Functionalized with Organic Layers HONGBIN YU, LAUREN WEBB, PEIGEN CAO, SANTIAGO SOLARES, RYAN RIES, WILLIAM GODDARD III, NATHAN LEWIS, JAMES HEATH, California Institute of Technology — High quality, high density Si nanowires can be used for making high density memory and logic circuits, and for biomolecule sensing when nanowires are selectively functionalized. An important step towards successful functionalization of Si wires is to control and understand the covalently bound monolayer of hydrocarbon molecules onto a silicon surface. Low temperature scanning tunneling microscopy (STM) data have been obtained on a series of alkyl group-terminated crystalline Si(111) surfaces that were prepared through a two-step chlorination/alkylation technique. The data from CH3terminated surface revealed a well-ordered structure commensurate with the atop sites of an unreconstructed 1x1 overlayer on...

Journal of Physical Chemistry B, 2000

... L. Sample, † Ryan Ries, Eileen M. Spain, and James R. Heath*. ... Prospects of Colloidal Nano... more ... L. Sample, † Ryan Ries, Eileen M. Spain, and James R. Heath*. ... Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications. Dmitri V. Talapin, Jong-Soo Lee, Maksym V. Kovalenko and Elena V. Shevchenko. Chemical Reviews 2010 110 (1), 389-458. ...

Journal of Physical Chemistry B, 2005

Low-temperature scanning tunneling microscopy (STM) has been used to image CH 3 -terminated Si(11... more Low-temperature scanning tunneling microscopy (STM) has been used to image CH 3 -terminated Si(111) surfaces that were prepared through a chlorination/alkylation procedure. The STM data revealed a wellordered structure commensurate with the atop sites of an unreconstructed 1 × 1 overlayer on the silicon (111) surface. Images collected at 4.7 K revealed bright spots, separated by 0.18 ( 0.01 nm, which are assigned to adjacent H atoms on the same methyl group. The C-H bonds in each methyl group were observed to be rotated by 7 ( 3°away from the center of an adjacent methyl group and toward an underlying Si atom. Hence, the predominant interaction that determines the surface structure arises from repulsions between hydrogen atoms on neighboring methyl groups, and secondary interactions unique to the surface are also evident.

Langmuir, 2004

A method for the spatially selective biofunctionalization of silicon micro- and nanostructures is... more A method for the spatially selective biofunctionalization of silicon micro- and nanostructures is reported, and results are presented for both single-crystal silicon (111) or (100) surfaces. An electroactive monolayer of hydroquinone was formed on the surface of H-terminated silicon working electrodes via an olefin reaction with UV-generated surface radicals. Molecules presenting either cyclopentadiene or a thiol group can be immobilized onto the regions where the hydroquinone has been oxidized. Molecular size and crystal orientation are evaluated as important factors that dictate the electrode stability in aqueous solution under anodic potentials. Monolayers composed of smaller molecules on (111) surfaces exhibit the highest packing density and are more effective in preventing anodic oxidation of the underlying substrate. Voltammetry, X-ray photoelectron spectroscopy, and atomic force and fluorescence microscopy are utilized to interrogate the kinetic rates of biofunctionalization, the extent of surface coverage, monolayer quality, and the spatial selectivity of the process.

Nano Letters, 2004

In this paper, we demonstrate a template-free, site-specific, and scalable electrochemical method... more In this paper, we demonstrate a template-free, site-specific, and scalable electrochemical method for the fabrication of individually addressable polyaniline nanoframework electrode junctions in a parallel-oriented array. These polyaniline nanoframeworks, which are ...

Journal of Physical Chemistry B, 2004

The structure and long-time dynamics of suspended lipid bilayers made of 1-stearoyl-2-oleoyl-sn-g... more The structure and long-time dynamics of suspended lipid bilayers made of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (SOPE) in the gel phase was interrogated using electrical measurements co-recorded with second harmonic generation (SHG) micrographs. SHG microscopy was shown to be an efficient method for distinguishing between the regions of bilayer and annulus as well as probing structural and dynamical variations within a single bilayer. Micromachined silicon chips and two types of plastic partitions, delrin and polyethylene, were investigated as substrate materials. Silicon chips yielded the most stable bilayers, lasting for 1 or 2 days. The membrane characteristics, including the amount of incorporated solvent within the bilayer, the dynamics of bilayer formation, and the stability of the bilayer, were found to be strongly substratedependent. In a second set of experiments, SHG-active membrane dyes, di-8-ANEPPS and di-4-ANEPPS, were used to interrogate the domain structure of the same suspended bilayers using scanning two-photon fluorescence (2PF) and SHG microscopy, again correlated with capacitance measurements. Using these dyes, an enhancement in the SHG signal due to membrane potential was recorded, and the rates of molecular diffusion for di-4-ANEPPS through the membrane were investigated. Polarization-resolved SHG imaging was used to determine the orientation of the dye molecules within the membrane.

Journal of Physical Chemistry B, 2002

The chemical interactions between single walled carbon nanotubes (SWNTs) and two structurally sim... more The chemical interactions between single walled carbon nanotubes (SWNTs) and two structurally similar polymers, poly{(m-phenylenevinylene)-co-[(2,5-dioctyloxy-p-phenylene)vinylene]}, or PmPV, and poly{(2,6pyridinylenevinylene)-co-[(2,5-dioctyloxy-p-phenylene)vinylene]}, or PPyPV, are investigated. The fundamental difference between these two polymers is that PPyPV is a base and is readily protonated via the addition of HCl. Both polymers promote chloroform solubilization of SWNTs. We find that the SWNT/PPyPV interaction lowers the pK a of PPyPV. Optoelectronic devices, fabricated from single polymer-wrapped SWNT structures, reveal a photogating effect on charge transport which can rectify or amplify current flow through the tubes. For PmPV wrapped tubes, the wavelength dependence of this effect correlates to the absorption spectrum of PmPV. For PPyPV, the wavelength dependence correlates with the absorption spectrum of protonated PPyPV, indicating that SWNTs assist in charge stabilization.

Chirality, 2002

The chiral recognition phenomenon observed in enantioselective excited-state energy transfer proc... more The chiral recognition phenomenon observed in enantioselective excited-state energy transfer processes currently requires the use of chiroptical spectroscopic techniques to probe the magnitude and sense of the discriminatory interactions. The use of chiroptical spectroscopic techniques limits the study of chiral recognition to those molecular species with strong absorption or emission dissymmetry factors. This study presents the theoretical and experimental methodology to determine the magnitude of chiral discriminatory interactions with unpolarized, steady-state luminescence measurements. Based on bimolecular luminescence quenching kinetics for a system containing chiral molecules, the Stern-Volmer equation is derived and contains a chiral discriminatory term for a system containing a chiral but racemic luminophore and an enantiomerically resolved quencher species. The utility of this methodology is confirmed by examining the enantioselective excited-state quenching between several Ln(dpa) complexes (where Ln = Eu3+, Tb3+, or Dy3+ and dpa = pyridine-2,6-dicarboxylate) acting as the energy donor and either racemic or enantiomerically resolved [Co(dach)3]3+ (where dach = trans-1R,2R (or 1S,2S)-diaminocyclohexane) acting as the energy acceptor in an aqueous solution. The results of this study confirm the utility of unpolarized, steady-state luminescence measurements as a probe of chiral discriminatory behavior. Chirality 14:456–464, 2002. © 2002 Wiley-Liss, Inc.

The Journal of Physical Chemistry B, 2002

The chemical interactions between single walled carbon nanotubes (SWNTs) and two structurally sim... more The chemical interactions between single walled carbon nanotubes (SWNTs) and two structurally similar polymers, poly{(m-phenylenevinylene)-co-[(2,5-dioctyloxy-p-phenylene)vinylene]}, or PmPV, and poly{(2,6pyridinylenevinylene)-co-[(2,5-dioctyloxy-p-phenylene)vinylene]}, or PPyPV, are investigated. The fundamental difference between these two polymers is that PPyPV is a base and is readily protonated via the addition of HCl. Both polymers promote chloroform solubilization of SWNTs. We find that the SWNT/PPyPV interaction lowers the pK a of PPyPV. Optoelectronic devices, fabricated from single polymer-wrapped SWNT structures, reveal a photogating effect on charge transport which can rectify or amplify current flow through the tubes. For PmPV wrapped tubes, the wavelength dependence of this effect correlates to the absorption spectrum of PmPV. For PPyPV, the wavelength dependence correlates with the absorption spectrum of protonated PPyPV, indicating that SWNTs assist in charge stabilization.

The Journal of Physical Chemistry B

... L. Sample, † Ryan Ries, Eileen M. Spain, and James R. Heath*. ... Prospects of Colloidal Nano... more ... L. Sample, † Ryan Ries, Eileen M. Spain, and James R. Heath*. ... Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications. Dmitri V. Talapin, Jong-Soo Lee, Maksym V. Kovalenko and Elena V. Shevchenko. Chemical Reviews 2010 110 (1), 389-458. ...

Langmuir, 2004

A method for the spatially selective biofunctionalization of silicon micro-and nanostructures is ... more A method for the spatially selective biofunctionalization of silicon micro-and nanostructures is reported, and results are presented for both single-crystal silicon (111) or (100) surfaces. An electroactive monolayer of hydroquinone was formed on the surface of H-terminated silicon working electrodes via an olefin reaction with UV-generated surface radicals. Molecules presenting either cyclopentadiene or a thiol group can be immobilized onto the regions where the hydroquinone has been oxidized. Molecular size and crystal orientation are evaluated as important factors that dictate the electrode stability in aqueous solution under anodic potentials. Monolayers composed of smaller molecules on (111) surfaces exhibit the highest packing density and are more effective in preventing anodic oxidation of the underlying substrate. Voltammetry, X-ray photoelectron spectroscopy, and atomic force and fluorescence microscopy are utilized to interrogate the kinetic rates of biofunctionalization, the extent of surface coverage, monolayer quality, and the spatial selectivity of the process.

Electrochimica Acta, 2006

A novel and sensitive electrochemical DNA biosensor based on electrochemically fabricated polyani... more A novel and sensitive electrochemical DNA biosensor based on electrochemically fabricated polyaniline nanowire and methylene blue for DNA hybridization detection is presented. Nanowires of conducting polymers were directly synthesized through a three-step electrochemical deposition procedure in an aniline-containing electrolyte solution, by using the glassy carbon electrode (GCE) as the working electrode. The morphology of the polyaniline films was examined using a field emission scanning electron microscope (SEM). The diameters of the nanowires range from 80 to 100 nm. The polyaniline nanowires-coated electrode exhibited very good electrochemical conductivity. Oligonucleotides with phosphate groups at the 5 end were covalently linked onto the amino groups of polyaniline nanowires on the electrode. The hybridization events were monitored with differential pulse voltammetry (DPV) measurement using methylene blue (MB) as an indicator. The approach described here can effectively discriminate complementary from non-complementary DNA sequence, with a detection limit of 1.0 × 10 −12 mol l −1 of complementary target, suggesting that the polyaniline nanowires hold great promises for sensitive electrochemical biosensor applications.

Chirality, 2002

The chiral recognition phenomenon observed in enantioselective excited-state energy transfer proc... more The chiral recognition phenomenon observed in enantioselective excited-state energy transfer processes currently requires the use of chiroptical spectroscopic techniques to probe the magnitude and sense of the discriminatory interactions. The use of chiroptical spectroscopic techniques limits the study of chiral recognition to those molecular species with strong absorption or emission dissymmetry factors. This study presents the theoretical and experimental methodology to determine the magnitude of chiral discriminatory interactions with unpolarized, steady-state luminescence measurements. Based on bimolecular luminescence quenching kinetics for a system containing chiral molecules, the Stern-Volmer equation is derived and contains a chiral discriminatory term for a system containing a chiral but racemic luminophore and an enantiomerically resolved quencher species. The utility of this methodology is confirmed by examining the enantioselective excited-state quenching between several Lndpa 3À 3 complexes (where Ln = Eu 3+ , Tb 3+ , or Dy 3+ and dpa = pyridine-2,6-dicarboxylate) acting as the energy donor and either racemic or enantiomerically resolved Codach 3 3 (where dach = trans-1R,2R (or 1S,2S)-diaminocyclohexane) acting as the energy acceptor in an aqueous solution. The results of this study confirm the utility of unpolarized, steady-state luminescence measurements as a probe of chiral discriminatory behavior. Chirality 14:456À464, 2002.

The Journal of Physical Chemistry B, 2004

The structure and long-time dynamics of suspended lipid bilayers made of 1-stearoyl-2-oleoyl-sn-g... more The structure and long-time dynamics of suspended lipid bilayers made of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (SOPE) in the gel phase was interrogated using electrical measurements co-recorded with second harmonic generation (SHG) micrographs. SHG microscopy was shown to be an efficient method for distinguishing between the regions of bilayer and annulus as well as probing structural and dynamical variations within a single bilayer. Micromachined silicon chips and two types of plastic partitions, delrin and polyethylene, were investigated as substrate materials. Silicon chips yielded the most stable bilayers, lasting for 1 or 2 days. The membrane characteristics, including the amount of incorporated solvent within the bilayer, the dynamics of bilayer formation, and the stability of the bilayer, were found to be strongly substratedependent. In a second set of experiments, SHG-active membrane dyes, di-8-ANEPPS and di-4-ANEPPS, were used to interrogate the domain structure of the same suspended bilayers using scanning two-photon fluorescence (2PF) and SHG microscopy, again correlated with capacitance measurements. Using these dyes, an enhancement in the SHG signal due to membrane potential was recorded, and the rates of molecular diffusion for di-4-ANEPPS through the membrane were investigated. Polarization-resolved SHG imaging was used to determine the orientation of the dye molecules within the membrane.

Low-temperature scanning tunneling microscopy (STM) has been used to image CH3-terminated Si(111)... more Low-temperature scanning tunneling microscopy (STM) has been used to image CH3-terminated Si(111) surfaces that were prepared through a chlorination/alkylation procedure. The STM data revealed a well-ordered structure commensurate with the atop sites of an unreconstructed 1 1 overlayer on the silicon (111) surface. Images collected at 4.7 K revealed bright spots, separated by 0.18 ( 0.01 nm, which are assigned to adjacent H atoms on the same methyl group. The C-H bonds in each methyl group were observed to be rotated by 7 ( 3 ° away from the center of an adjacent methyl group and toward an underlying Si atom. Hence, the predominant interaction that determines the surface structure arises from repulsions between hydrogen atoms on neighboring methyl groups, and secondary interactions unique to the surface are also evident. Hydrogen-terminated (111)-oriented Si surfaces are well documented to have a low number of structural and electrically active defect sites.1,2 However, these surfac...

Underwater imaging of the air environment is described with particular attention given to the opt... more Underwater imaging of the air environment is described with particular attention given to the optical problems of near-horizon viewing. These include severe chromatic aberration from transmission through the seawater wedge, the horizon distortion effect, ...

Bulletin of the American Physical Society, 2005

Submitted for the MAR05 Meeting of The American Physical Society STM Characterization of Si Surfa... more Submitted for the MAR05 Meeting of The American Physical Society STM Characterization of Si Surface Functionalized with Organic Layers HONGBIN YU, LAUREN WEBB, PEIGEN CAO, SANTIAGO SOLARES, RYAN RIES, WILLIAM GODDARD III, NATHAN LEWIS, JAMES HEATH, California Institute of Technology — High quality, high density Si nanowires can be used for making high density memory and logic circuits, and for biomolecule sensing when nanowires are selectively functionalized. An important step towards successful functionalization of Si wires is to control and understand the covalently bound monolayer of hydrocarbon molecules onto a silicon surface. Low temperature scanning tunneling microscopy (STM) data have been obtained on a series of alkyl group-terminated crystalline Si(111) surfaces that were prepared through a two-step chlorination/alkylation technique. The data from CH3terminated surface revealed a well-ordered structure commensurate with the atop sites of an unreconstructed 1x1 overlayer on...

Journal of Physical Chemistry B, 2000

... L. Sample, † Ryan Ries, Eileen M. Spain, and James R. Heath*. ... Prospects of Colloidal Nano... more ... L. Sample, † Ryan Ries, Eileen M. Spain, and James R. Heath*. ... Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications. Dmitri V. Talapin, Jong-Soo Lee, Maksym V. Kovalenko and Elena V. Shevchenko. Chemical Reviews 2010 110 (1), 389-458. ...

Journal of Physical Chemistry B, 2005

Low-temperature scanning tunneling microscopy (STM) has been used to image CH 3 -terminated Si(11... more Low-temperature scanning tunneling microscopy (STM) has been used to image CH 3 -terminated Si(111) surfaces that were prepared through a chlorination/alkylation procedure. The STM data revealed a wellordered structure commensurate with the atop sites of an unreconstructed 1 × 1 overlayer on the silicon (111) surface. Images collected at 4.7 K revealed bright spots, separated by 0.18 ( 0.01 nm, which are assigned to adjacent H atoms on the same methyl group. The C-H bonds in each methyl group were observed to be rotated by 7 ( 3°away from the center of an adjacent methyl group and toward an underlying Si atom. Hence, the predominant interaction that determines the surface structure arises from repulsions between hydrogen atoms on neighboring methyl groups, and secondary interactions unique to the surface are also evident.

Langmuir, 2004

A method for the spatially selective biofunctionalization of silicon micro- and nanostructures is... more A method for the spatially selective biofunctionalization of silicon micro- and nanostructures is reported, and results are presented for both single-crystal silicon (111) or (100) surfaces. An electroactive monolayer of hydroquinone was formed on the surface of H-terminated silicon working electrodes via an olefin reaction with UV-generated surface radicals. Molecules presenting either cyclopentadiene or a thiol group can be immobilized onto the regions where the hydroquinone has been oxidized. Molecular size and crystal orientation are evaluated as important factors that dictate the electrode stability in aqueous solution under anodic potentials. Monolayers composed of smaller molecules on (111) surfaces exhibit the highest packing density and are more effective in preventing anodic oxidation of the underlying substrate. Voltammetry, X-ray photoelectron spectroscopy, and atomic force and fluorescence microscopy are utilized to interrogate the kinetic rates of biofunctionalization, the extent of surface coverage, monolayer quality, and the spatial selectivity of the process.

Nano Letters, 2004

In this paper, we demonstrate a template-free, site-specific, and scalable electrochemical method... more In this paper, we demonstrate a template-free, site-specific, and scalable electrochemical method for the fabrication of individually addressable polyaniline nanoframework electrode junctions in a parallel-oriented array. These polyaniline nanoframeworks, which are ...

Journal of Physical Chemistry B, 2004

The structure and long-time dynamics of suspended lipid bilayers made of 1-stearoyl-2-oleoyl-sn-g... more The structure and long-time dynamics of suspended lipid bilayers made of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (SOPE) in the gel phase was interrogated using electrical measurements co-recorded with second harmonic generation (SHG) micrographs. SHG microscopy was shown to be an efficient method for distinguishing between the regions of bilayer and annulus as well as probing structural and dynamical variations within a single bilayer. Micromachined silicon chips and two types of plastic partitions, delrin and polyethylene, were investigated as substrate materials. Silicon chips yielded the most stable bilayers, lasting for 1 or 2 days. The membrane characteristics, including the amount of incorporated solvent within the bilayer, the dynamics of bilayer formation, and the stability of the bilayer, were found to be strongly substratedependent. In a second set of experiments, SHG-active membrane dyes, di-8-ANEPPS and di-4-ANEPPS, were used to interrogate the domain structure of the same suspended bilayers using scanning two-photon fluorescence (2PF) and SHG microscopy, again correlated with capacitance measurements. Using these dyes, an enhancement in the SHG signal due to membrane potential was recorded, and the rates of molecular diffusion for di-4-ANEPPS through the membrane were investigated. Polarization-resolved SHG imaging was used to determine the orientation of the dye molecules within the membrane.

Journal of Physical Chemistry B, 2002

The chemical interactions between single walled carbon nanotubes (SWNTs) and two structurally sim... more The chemical interactions between single walled carbon nanotubes (SWNTs) and two structurally similar polymers, poly{(m-phenylenevinylene)-co-[(2,5-dioctyloxy-p-phenylene)vinylene]}, or PmPV, and poly{(2,6pyridinylenevinylene)-co-[(2,5-dioctyloxy-p-phenylene)vinylene]}, or PPyPV, are investigated. The fundamental difference between these two polymers is that PPyPV is a base and is readily protonated via the addition of HCl. Both polymers promote chloroform solubilization of SWNTs. We find that the SWNT/PPyPV interaction lowers the pK a of PPyPV. Optoelectronic devices, fabricated from single polymer-wrapped SWNT structures, reveal a photogating effect on charge transport which can rectify or amplify current flow through the tubes. For PmPV wrapped tubes, the wavelength dependence of this effect correlates to the absorption spectrum of PmPV. For PPyPV, the wavelength dependence correlates with the absorption spectrum of protonated PPyPV, indicating that SWNTs assist in charge stabilization.

Chirality, 2002

The chiral recognition phenomenon observed in enantioselective excited-state energy transfer proc... more The chiral recognition phenomenon observed in enantioselective excited-state energy transfer processes currently requires the use of chiroptical spectroscopic techniques to probe the magnitude and sense of the discriminatory interactions. The use of chiroptical spectroscopic techniques limits the study of chiral recognition to those molecular species with strong absorption or emission dissymmetry factors. This study presents the theoretical and experimental methodology to determine the magnitude of chiral discriminatory interactions with unpolarized, steady-state luminescence measurements. Based on bimolecular luminescence quenching kinetics for a system containing chiral molecules, the Stern-Volmer equation is derived and contains a chiral discriminatory term for a system containing a chiral but racemic luminophore and an enantiomerically resolved quencher species. The utility of this methodology is confirmed by examining the enantioselective excited-state quenching between several Ln(dpa) complexes (where Ln = Eu3+, Tb3+, or Dy3+ and dpa = pyridine-2,6-dicarboxylate) acting as the energy donor and either racemic or enantiomerically resolved [Co(dach)3]3+ (where dach = trans-1R,2R (or 1S,2S)-diaminocyclohexane) acting as the energy acceptor in an aqueous solution. The results of this study confirm the utility of unpolarized, steady-state luminescence measurements as a probe of chiral discriminatory behavior. Chirality 14:456–464, 2002. © 2002 Wiley-Liss, Inc.