D. Dunlap, L. Schein, A. Tyutnev, V. S. Saenko, E. Pozhidaev, P. Parris, D. Weiss
The mechanism of charge transport in molecularly doped polymers has been the subject of much discussion over the years. In this paper, data obtained from a new experimental variant of the time-of-flight (TOF) technique, called TOF1a, are compared to the predictions of a two-layer multiple trapping model (MTM) with an exponential distribution of traps. In the recently introduced TOF1a experimental variant, the charge generation depth is varied continuously, from surface generation to bulk generation, by varying the energy of the electron-beam excitation source. This produces systematic changes in the shape of the current transient that can be compared to predictions of the two-layer MTM. In the model, one additional assumption is added to the homogeneous MTM, namely: that there exists a surface region, on the order of a micrometer thick, in which the trap distribution is identical to the bulk, but has a higher trap concentration. We find that the characteristic experimental features of an initial spike, a ...
{"title":"Two-Layer Mutiple Trapping Model for Universal Current Transients in Molecularly Doped Polymers","authors":"D. Dunlap, L. Schein, A. Tyutnev, V. S. Saenko, E. Pozhidaev, P. Parris, D. Weiss","doi":"10.1021/JP1010132","DOIUrl":"https://doi.org/10.1021/JP1010132","url":null,"abstract":"The mechanism of charge transport in molecularly doped polymers has been the subject of much discussion over the years. In this paper, data obtained from a new experimental variant of the time-of-flight (TOF) technique, called TOF1a, are compared to the predictions of a two-layer multiple trapping model (MTM) with an exponential distribution of traps. In the recently introduced TOF1a experimental variant, the charge generation depth is varied continuously, from surface generation to bulk generation, by varying the energy of the electron-beam excitation source. This produces systematic changes in the shape of the current transient that can be compared to predictions of the two-layer MTM. In the model, one additional assumption is added to the homogeneous MTM, namely: that there exists a surface region, on the order of a micrometer thick, in which the trap distribution is identical to the bulk, but has a higher trap concentration. We find that the characteristic experimental features of an initial spike, a ...","PeriodicalId":58,"journal":{"name":"The Journal of Physical Chemistry ","volume":null,"pages":null},"PeriodicalIF":2.781,"publicationDate":"2010-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89155843","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ram Subbaraman, D. Strmcnik, V. Stamenkovic, N. Markovic
A voltammetric fingerprinting approach has been used to probe the nature of Pt−Nafion three phase interfaces for Pt(hkl) and polycrystalline platinum surfaces. Nature of adsorbing species is identified as the sulfonate anions via CO charge displacement technique. The affinity for the sulfonate anions to adsorb on the electrode surface is investigated. Adsorption strength of the sulfonate anions with the electrode surface is compared with other strongly adsorbing anions such as (bi) sulfates and chlorides. Various factors that influence the adsorption properties of the sulfonate anions are studied. Nature and strength of the anion interaction with various surface geometries is also discussed. A physical model is presented to describe the observed phenomena.
{"title":"Three Phase Interfaces at Electrified Metal−Solid Electrolyte Systems 1. Study of the Pt(hkl)−Nafion Interface","authors":"Ram Subbaraman, D. Strmcnik, V. Stamenkovic, N. Markovic","doi":"10.1021/JP100814X","DOIUrl":"https://doi.org/10.1021/JP100814X","url":null,"abstract":"A voltammetric fingerprinting approach has been used to probe the nature of Pt−Nafion three phase interfaces for Pt(hkl) and polycrystalline platinum surfaces. Nature of adsorbing species is identified as the sulfonate anions via CO charge displacement technique. The affinity for the sulfonate anions to adsorb on the electrode surface is investigated. Adsorption strength of the sulfonate anions with the electrode surface is compared with other strongly adsorbing anions such as (bi) sulfates and chlorides. Various factors that influence the adsorption properties of the sulfonate anions are studied. Nature and strength of the anion interaction with various surface geometries is also discussed. A physical model is presented to describe the observed phenomena.","PeriodicalId":58,"journal":{"name":"The Journal of Physical Chemistry ","volume":null,"pages":null},"PeriodicalIF":2.781,"publicationDate":"2010-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89151433","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Bennett N. Walker, Jessica A. Stolee, Deanna L. Pickel, S. Retterer, A. Vertes
Nanostructures that have dimensions commensurate with the wavelength of the electromagnetic radiation exhibit near-field effects and, as optical antennas, can couple laser radiation to the local environment. Laser-induced silicon microcolumn arrays behave as nanophotonic ion sources that can be modulated by rotating the plane of light polarization. However, the limited range of surface morphologies available for these substrates makes it difficult to study the underlying mechanism that governs ion production. Here we demonstrate that nanopost arrays (NAPAs) can be tailored to exhibit resonant ion production. Ion yields from posts with subwavelength diameter show sharp resonances at high aspect ratios. The resonant enhancement in ion intensities can be modulated by adjusting the periodicity. In addition to strong molecular ion formation, the presence of high-energy fragmentation channels is observed. Ion yields from NAPAs exhibit dramatic differences for p- and s-polarized laser beams, indicating that ener...
{"title":"Tailored Silicon Nanopost Arrays for Resonant Nanophotonic Ion Production","authors":"Bennett N. Walker, Jessica A. Stolee, Deanna L. Pickel, S. Retterer, A. Vertes","doi":"10.1021/JP9110103","DOIUrl":"https://doi.org/10.1021/JP9110103","url":null,"abstract":"Nanostructures that have dimensions commensurate with the wavelength of the electromagnetic radiation exhibit near-field effects and, as optical antennas, can couple laser radiation to the local environment. Laser-induced silicon microcolumn arrays behave as nanophotonic ion sources that can be modulated by rotating the plane of light polarization. However, the limited range of surface morphologies available for these substrates makes it difficult to study the underlying mechanism that governs ion production. Here we demonstrate that nanopost arrays (NAPAs) can be tailored to exhibit resonant ion production. Ion yields from posts with subwavelength diameter show sharp resonances at high aspect ratios. The resonant enhancement in ion intensities can be modulated by adjusting the periodicity. In addition to strong molecular ion formation, the presence of high-energy fragmentation channels is observed. Ion yields from NAPAs exhibit dramatic differences for p- and s-polarized laser beams, indicating that ener...","PeriodicalId":58,"journal":{"name":"The Journal of Physical Chemistry ","volume":null,"pages":null},"PeriodicalIF":2.781,"publicationDate":"2010-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77124939","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
B. Fabre, S. Cordier, Y. Molard, C. Perrin, S. Ababou-Girard, C. Godet
Octahedral molybdenum cluster cores [Mo6I8]4+ have been attached in apical positions to p- and n-type Si(111) surfaces through complexation with a pyridine-terminated organic monolayer (2 × 1014 cm−2), which was previously covalently bound to hydrogen-terminated Si(111). This grafting procedure resulted in about a 4 nm thick Mo6-terminated layer. Similar XPS results were found for p- and n-type samples, suggesting that the grafting efficiency and composition of the resulting layers do not depend significantly on the doping type of the surface. The cluster footprint of 10 nm2 indicates a fairly dense molecular packing on the Si(111) surface. The electrochemistry of such Mo6-modified surfaces in acetonitrile was characterized by a single irreversible oxidation peak at 0.92 V versus saturated calomel electrode (SCE) and flat band potential Efb values of −0.55 ± 0.05 V and 0.04 ± 0.05 V for the modified n- and p-type surfaces, respectively. The derivatization of silicon surfaces by Mo6 introduces surface stat...
{"title":"Electrochemical and Charge Transport Behavior of Molybdenum-Based Metallic Cluster Layers Immobilized on Modified n- and p-Type Si(111) Surfaces","authors":"B. Fabre, S. Cordier, Y. Molard, C. Perrin, S. Ababou-Girard, C. Godet","doi":"10.1021/JP903205A","DOIUrl":"https://doi.org/10.1021/JP903205A","url":null,"abstract":"Octahedral molybdenum cluster cores [Mo6I8]4+ have been attached in apical positions to p- and n-type Si(111) surfaces through complexation with a pyridine-terminated organic monolayer (2 × 1014 cm−2), which was previously covalently bound to hydrogen-terminated Si(111). This grafting procedure resulted in about a 4 nm thick Mo6-terminated layer. Similar XPS results were found for p- and n-type samples, suggesting that the grafting efficiency and composition of the resulting layers do not depend significantly on the doping type of the surface. The cluster footprint of 10 nm2 indicates a fairly dense molecular packing on the Si(111) surface. The electrochemistry of such Mo6-modified surfaces in acetonitrile was characterized by a single irreversible oxidation peak at 0.92 V versus saturated calomel electrode (SCE) and flat band potential Efb values of −0.55 ± 0.05 V and 0.04 ± 0.05 V for the modified n- and p-type surfaces, respectively. The derivatization of silicon surfaces by Mo6 introduces surface stat...","PeriodicalId":58,"journal":{"name":"The Journal of Physical Chemistry ","volume":null,"pages":null},"PeriodicalIF":2.781,"publicationDate":"2009-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75147285","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
E. Pouzet, V. D. Cupere, C. Heintz, J. W. Andreasen, D. Breiby, M. Nielsen, P. Viville, R. Lazzaroni, G. Gbabode, Y. Geerts
A convenient method to induce face-on orientation of an alkoxy phtalocyanine discotic mesogen is described. The alignment is imposed by the confinement of the discotic thin films with a top sacrificial polymer layer that is easily removed by washing with a selective solvent, after thermal annealing. Thin films have been characterized by optical and atomic force microscopy, UV-Vis absorption spectroscopy, and grazing incidence wide angle X-ray scattering. The data converge in showing the central role of the sacrificial layer in promoting alignment with the planar molecules orienting parallel to the substrate in an essentially homeotropic arrangement over large lateral length scales and the persistence of this desirable alignment after removal of the layer.
{"title":"Homeotropic Alignment of a Discotic Liquid Crystal Induced by a Sacrificial Layer","authors":"E. Pouzet, V. D. Cupere, C. Heintz, J. W. Andreasen, D. Breiby, M. Nielsen, P. Viville, R. Lazzaroni, G. Gbabode, Y. Geerts","doi":"10.1021/JP9035343","DOIUrl":"https://doi.org/10.1021/JP9035343","url":null,"abstract":"A convenient method to induce face-on orientation of an alkoxy phtalocyanine discotic mesogen is described. The alignment is imposed by the confinement of the discotic thin films with a top sacrificial polymer layer that is easily removed by washing with a selective solvent, after thermal annealing. Thin films have been characterized by optical and atomic force microscopy, UV-Vis absorption spectroscopy, and grazing incidence wide angle X-ray scattering. The data converge in showing the central role of the sacrificial layer in promoting alignment with the planar molecules orienting parallel to the substrate in an essentially homeotropic arrangement over large lateral length scales and the persistence of this desirable alignment after removal of the layer.","PeriodicalId":58,"journal":{"name":"The Journal of Physical Chemistry ","volume":null,"pages":null},"PeriodicalIF":2.781,"publicationDate":"2009-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72664486","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Overbury, Xiaoxing Wang, Jason C. Clark, Xiaoliang Ma, Xiaochun Xu, C. Song, V. Schwartz
An infrared study has been conducted on CO{sub 2} sorption into nanoporous CO{sub 2} 'molecular basket' sorbents prepared by loading polyethylenimine (PEI) into mesoporous molecular sieve SBA-15. IR results from DRIFTS showed that a part of loaded PEI is anchored on the surface of SBA-15 through the interaction between amine groups and isolated surface silanol groups. Raising the temperature from 25 to 75 C increased the molecular flexibility of PEI loaded in the mesopore channels, which may partly contribute to the increase of CO{sub 2} sorption capacity at higher temperatures. CO{sub 2} sorption/desorption behavior studied by in situ transmission FTIR showed that CO{sub 2} is sorbed on amine sites through the formation of alkylammonium carbamates and absorbed into the multiple layers of PEI located in mesopores of SBA-15. A new observation by in situ IR is that two broad IR bands emerged at 2450 and 2160 cm{sup -1} with CO{sub 2} flowing over PEI(50)/SBA-15, which could be attributed to chemically sorbed CO{sub 2} species on PEI molecules inside the mesopores of SBA-15. The intensities of these two bands also increased with increasing CO{sub 2} exposure time and with raising CO{sub 2} sorption temperature. By comparison of the CO{sub 2} sorptionmore » rate at 25 and 75 C in terms of differential IR intensities, it was found that CO{sub 2} sorption over molecular basket sorbent includes two rate regimes which suggest two distinct steps: rapid sorption on exposed outer surface layers of PEI (controlled by sorption affinity or thermodynamics) and the diffusion and sorption inside the bulk of multiple layers of PEI (controlled by diffusion). The sorption of CO{sub 2} is reversible at 75 C. Comparative IR examination of the CO{sub 2} sorption/desorption spectra on dry and prewetted PEI/SBA-15 sorbent revealed that presorbed water does not significantly affect the CO{sub 2}-amine interaction patterns.« less
{"title":"Infrared Study of CO2 Sorption over ?Molecular Basket? Sorbent Consisting of Polyethylenimine-Modified Mesoporous Molecular Sieve","authors":"S. Overbury, Xiaoxing Wang, Jason C. Clark, Xiaoliang Ma, Xiaochun Xu, C. Song, V. Schwartz","doi":"10.1021/JP809946Y","DOIUrl":"https://doi.org/10.1021/JP809946Y","url":null,"abstract":"An infrared study has been conducted on CO{sub 2} sorption into nanoporous CO{sub 2} 'molecular basket' sorbents prepared by loading polyethylenimine (PEI) into mesoporous molecular sieve SBA-15. IR results from DRIFTS showed that a part of loaded PEI is anchored on the surface of SBA-15 through the interaction between amine groups and isolated surface silanol groups. Raising the temperature from 25 to 75 C increased the molecular flexibility of PEI loaded in the mesopore channels, which may partly contribute to the increase of CO{sub 2} sorption capacity at higher temperatures. CO{sub 2} sorption/desorption behavior studied by in situ transmission FTIR showed that CO{sub 2} is sorbed on amine sites through the formation of alkylammonium carbamates and absorbed into the multiple layers of PEI located in mesopores of SBA-15. A new observation by in situ IR is that two broad IR bands emerged at 2450 and 2160 cm{sup -1} with CO{sub 2} flowing over PEI(50)/SBA-15, which could be attributed to chemically sorbed CO{sub 2} species on PEI molecules inside the mesopores of SBA-15. The intensities of these two bands also increased with increasing CO{sub 2} exposure time and with raising CO{sub 2} sorption temperature. By comparison of the CO{sub 2} sorptionmore » rate at 25 and 75 C in terms of differential IR intensities, it was found that CO{sub 2} sorption over molecular basket sorbent includes two rate regimes which suggest two distinct steps: rapid sorption on exposed outer surface layers of PEI (controlled by sorption affinity or thermodynamics) and the diffusion and sorption inside the bulk of multiple layers of PEI (controlled by diffusion). The sorption of CO{sub 2} is reversible at 75 C. Comparative IR examination of the CO{sub 2} sorption/desorption spectra on dry and prewetted PEI/SBA-15 sorbent revealed that presorbed water does not significantly affect the CO{sub 2}-amine interaction patterns.« less","PeriodicalId":58,"journal":{"name":"The Journal of Physical Chemistry ","volume":null,"pages":null},"PeriodicalIF":2.781,"publicationDate":"2009-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87858644","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Neshyba, E. Nugent, Martina Roeselová, P. Jungwirth
Molecular dynamics simulations of ice Ih in a slab geometry with a free basal (0001) surface are carried out at 250 K in order to study the structure and dynamics of the ice/vapor interface, focusing on processes associated with sublimation and deposition. Surface melting, which results in the formation of a quasi-liquid layer, causes about 8% of the molecules originally constituting the surface bilayer to leave their crystal lattice positions and form an outer, highly mobile sublayer. Molecules in this sublayer typically form two H bonds, predominantly in a dangling-O orientation, with preference for a dangling-H orientation also evident. The remaining 92% of the quasi-liquid layer molecules belong to the deeper, more crystalline sublayer, typically forming three H bonds in an orientational distribution that closely resembles bulk crystalline ice. Transitions between the quasi-liquid layer and the first underlying crystalline bilayer were also observed on the molecular dynamics simulation time scale, alb...
{"title":"Molecular Dynamics study of ice-vapor interactions via the quasi-liquid layer","authors":"S. Neshyba, E. Nugent, Martina Roeselová, P. Jungwirth","doi":"10.1021/JP810589A","DOIUrl":"https://doi.org/10.1021/JP810589A","url":null,"abstract":"Molecular dynamics simulations of ice Ih in a slab geometry with a free basal (0001) surface are carried out at 250 K in order to study the structure and dynamics of the ice/vapor interface, focusing on processes associated with sublimation and deposition. Surface melting, which results in the formation of a quasi-liquid layer, causes about 8% of the molecules originally constituting the surface bilayer to leave their crystal lattice positions and form an outer, highly mobile sublayer. Molecules in this sublayer typically form two H bonds, predominantly in a dangling-O orientation, with preference for a dangling-H orientation also evident. The remaining 92% of the quasi-liquid layer molecules belong to the deeper, more crystalline sublayer, typically forming three H bonds in an orientational distribution that closely resembles bulk crystalline ice. Transitions between the quasi-liquid layer and the first underlying crystalline bilayer were also observed on the molecular dynamics simulation time scale, alb...","PeriodicalId":58,"journal":{"name":"The Journal of Physical Chemistry ","volume":null,"pages":null},"PeriodicalIF":2.781,"publicationDate":"2009-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74862795","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Y. Otsuka, Y. Okamoto, H. Y. Akiyama, K. Umekita, Y. Tachibana, S. Kuwabata
Formation of nanostructured polythiophene/TiO2 heterojunction films, using photoinduced polymerization of thiophene inside TiO2 nanopores, was investigated. The resultant film possesses nanohybridization and electronic connection within the TiO2 nanoporous domain. Photopolymerization proceeded in three stages: (i) photoexcitation of bithiophene covalently attached to the TiO2 surface, (ii) an electron injection reaction from the surface attached thiophene to the TiO2, and (iii) an electron transfer from a thiophene reactant in an electrolyte to the surface-attached bithiophene. Initial rapid photopolymerization and subsequent slow polymer growth were explained by analysis of a series of experiments, e.g., with respect to light irradiation time, applied bias, electrolyte types, thiophene reactant type, and their morphology. Electrochemical measurements for the bithiophene adsorbed on TiO2 revealed a wide distribution of redox potentials. This was explained by influence of the local electric field on the TiO2 surface in addition to strong interaction between the surfacebound bithiophene and the TiO2. The nanohybrid film was applied to a sensitized-type photoelectrochemical solar cell, substantiating direct application of the nanohybrid film to electronic devices. The solar cell performance was closely associated with the interfacial structure in the nanohybrid film and the photopolymerization degree.
{"title":"Photoinduced Formation of Polythiophene/TiO2 Nanohybrid Heterojunction Films for Solar Cell Applications","authors":"Y. Otsuka, Y. Okamoto, H. Y. Akiyama, K. Umekita, Y. Tachibana, S. Kuwabata","doi":"10.1021/JP7099064","DOIUrl":"https://doi.org/10.1021/JP7099064","url":null,"abstract":"Formation of nanostructured polythiophene/TiO2 heterojunction films, using photoinduced polymerization of thiophene inside TiO2 nanopores, was investigated. The resultant film possesses nanohybridization and electronic connection within the TiO2 nanoporous domain. Photopolymerization proceeded in three stages: (i) photoexcitation of bithiophene covalently attached to the TiO2 surface, (ii) an electron injection reaction from the surface attached thiophene to the TiO2, and (iii) an electron transfer from a thiophene reactant in an electrolyte to the surface-attached bithiophene. Initial rapid photopolymerization and subsequent slow polymer growth were explained by analysis of a series of experiments, e.g., with respect to light irradiation time, applied bias, electrolyte types, thiophene reactant type, and their morphology. Electrochemical measurements for the bithiophene adsorbed on TiO2 revealed a wide distribution of redox potentials. This was explained by influence of the local electric field on the TiO2 surface in addition to strong interaction between the surfacebound bithiophene and the TiO2. The nanohybrid film was applied to a sensitized-type photoelectrochemical solar cell, substantiating direct application of the nanohybrid film to electronic devices. The solar cell performance was closely associated with the interfacial structure in the nanohybrid film and the photopolymerization degree.","PeriodicalId":58,"journal":{"name":"The Journal of Physical Chemistry ","volume":null,"pages":null},"PeriodicalIF":2.781,"publicationDate":"2008-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89364992","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Hemmersam, K. Rechendorff, F. Besenbacher, and Bengt Kasemo, Duncan S Sutherland
In this work, we have identified key parameters for controlling the surface density of ferritin on metal oxides and observed a conformational change of the protein shell of ferritin occurring exclusively at pH 4. The quartz crystal microbalance with dissipation (QCM-D) monitoring technique was used to examine protein adsorption on gold and Ti-, Si-, Ta-, Al-, and Nb-oxide surfaces. A comparative study of the adsorption to Ti-oxide was made using atomic force microscopy (AFM). The surface density of ferritin was controlled by a variation in the solution pH (from 2 to 8) and the isoelectric point (Ip) of the surface. On the basis of these findings, clear trends in the effect of electrostatic interactions between the ferritin proteins and between ferritin and the surface were found, making it possible to tune the surface density of ferritin through the choice of solution pH and the Ip of the surface. Furthermore, the influence of the pH on the viscoelastic properties of the adsorbed ferritin layer was examin...
{"title":"pH-Dependent Adsorption and Conformational Change of Ferritin Studied on Metal Oxide Surfaces by a Combination of QCM-D and AFM","authors":"A. Hemmersam, K. Rechendorff, F. Besenbacher, and Bengt Kasemo, Duncan S Sutherland","doi":"10.1021/JP072413T","DOIUrl":"https://doi.org/10.1021/JP072413T","url":null,"abstract":"In this work, we have identified key parameters for controlling the surface density of ferritin on metal oxides and observed a conformational change of the protein shell of ferritin occurring exclusively at pH 4. The quartz crystal microbalance with dissipation (QCM-D) monitoring technique was used to examine protein adsorption on gold and Ti-, Si-, Ta-, Al-, and Nb-oxide surfaces. A comparative study of the adsorption to Ti-oxide was made using atomic force microscopy (AFM). The surface density of ferritin was controlled by a variation in the solution pH (from 2 to 8) and the isoelectric point (Ip) of the surface. On the basis of these findings, clear trends in the effect of electrostatic interactions between the ferritin proteins and between ferritin and the surface were found, making it possible to tune the surface density of ferritin through the choice of solution pH and the Ip of the surface. Furthermore, the influence of the pH on the viscoelastic properties of the adsorbed ferritin layer was examin...","PeriodicalId":58,"journal":{"name":"The Journal of Physical Chemistry ","volume":null,"pages":null},"PeriodicalIF":2.781,"publicationDate":"2008-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88707806","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present a theoretical study of the structure, local curvature angles, and reactivity of cap-ended (7,0), defective and nondefective carbon nanotubes. We find that the most reactive sites are the atoms that form part of the caps even when the Stone-Wales defect is present. Each carbon in the carbon nanotube is located at the top of a pyramidal structure with three walls of 5-, 6-, or 7-carbon rings. Among the carbons making up the caps, the most reactive sites are the top pyramidal atoms between two 5-carbon rings and one 6-carbon ring and each 5-carbon ring has attached another 5-carbon ring. The least reactive sites are the top pyramidal atoms between three 6-carbon rings. The activity of each pyramidal structure is strongly correlated to its local curvature angle. The dissociation of one water molecule on the surface of the carbon nanotubes confirms the location of the most active site. The dissociation of water produces a hydroxyl group and a hydrogen atom united each to two adjacent carbon atoms. The dissociation process of water on carbon nanotubes is energetically favorable starting from the isolated molecules.
{"title":"Interaction of Water with Cap-Ended Defective and Non-Defective Small Carbon Nanotubes","authors":"J. Rivera, J. Rico, F. Starr","doi":"10.1021/JP075989R","DOIUrl":"https://doi.org/10.1021/JP075989R","url":null,"abstract":"We present a theoretical study of the structure, local curvature angles, and reactivity of cap-ended (7,0), defective and nondefective carbon nanotubes. We find that the most reactive sites are the atoms that form part of the caps even when the Stone-Wales defect is present. Each carbon in the carbon nanotube is located at the top of a pyramidal structure with three walls of 5-, 6-, or 7-carbon rings. Among the carbons making up the caps, the most reactive sites are the top pyramidal atoms between two 5-carbon rings and one 6-carbon ring and each 5-carbon ring has attached another 5-carbon ring. The least reactive sites are the top pyramidal atoms between three 6-carbon rings. The activity of each pyramidal structure is strongly correlated to its local curvature angle. The dissociation of one water molecule on the surface of the carbon nanotubes confirms the location of the most active site. The dissociation of water produces a hydroxyl group and a hydrogen atom united each to two adjacent carbon atoms. The dissociation process of water on carbon nanotubes is energetically favorable starting from the isolated molecules.","PeriodicalId":58,"journal":{"name":"The Journal of Physical Chemistry ","volume":null,"pages":null},"PeriodicalIF":2.781,"publicationDate":"2007-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83595311","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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