36 results on '"George Chumanov"'
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2. Hydrothermal synthesis of lanthanide rhenium oxides: Structures and magnetism of Ln2Re2O7(OH) (Ln = Pr, Nd) and Ln4Re2O11 (Ln = Eu, Tb)
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Yimei Wen, Mudithangani T.K. Kolambage, Kimberly Ivey, Joseph W. Kolis, Liurukara D. Sanjeewa, George Chumanov, Michael A. McGuire, and Colin D. McMillen
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Lanthanide ,Materials science ,Double bond ,Magnetism ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,Sesquioxide ,Materials Chemistry ,Hydrothermal synthesis ,Physical and Theoretical Chemistry ,chemistry.chemical_classification ,Rhenium ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Crystallography ,chemistry ,Ceramics and Composites ,0210 nano-technology ,Single crystal - Abstract
The reactions of Ln2O3 (Ln = La Lu) with ReO2 were examined in high temperature hydrothermal water (650 °C). In all cases the rhenium oxide was added in a three-fold excess. No external mineralizer was needed and the rhenate itself acted as a sufficient mineralizer to form high quality single crystals of several crystalline products. These form in good yield with compositions varying as a function of the size of the rare earth ion. The largest sesquioxide, La2O3, forms the well-known La4Re6O19 phase, but when Ln = Nd or Pr, a new product, Ln2Re2O7(OH), is isolated. Reactions with Ln = Sm Tb form Ln4Re2O11, and those with Dy Lu form Ln2ReO5. The new Ln2Re2O7(OH) series was characterized as a new structure type by single crystal X-ray diffraction. This structure features a tetrameric Re4O16 cluster embedded in a lanthanide oxide framework. Additional detailed structural data is also provided for Tb4Re2O11 and Eu4Re2O11, which were not previously reported for the Ln4Re2O11 family. In Ln2Re2O7(OH), no direct Re Re bond (Re Re = 2.60 A) is observed while Ln4Re2O11 appears to possess a rhenium-rhenium double bond with a Re Re distance of 2.42 A. Single crystal Raman data supports both of these characterizations. Magnetic data is reported for Ln2Re2O7(OH) and Tb4Re2O11, and their behavior appears to be dominated by the f-element magnetic moments. At low temperatures Tb4Re2O11 displays possible canted antiferromagnetic coupling.
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- 2019
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3. Strontium manganese vanadates from hydrothermal brines: Synthesis and structure of Sr2Mn2(V3O10)(VO4), Sr3Mn(V2O7)2, and Sr2Mn(VO4)2(OH)
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Colin D. McMillen, Rachel B. Getman, Steven Pellizzeri, Yimei Wen, Tiffany M. Smith Pellizzeri, Joseph W. Kolis, and George Chumanov
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Strontium ,Inorganic chemistry ,chemistry.chemical_element ,Infrared spectroscopy ,02 engineering and technology ,Manganese ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Inorganic Chemistry ,Tetragonal crystal system ,Crystallography ,chemistry ,Octahedron ,Materials Chemistry ,Ceramics and Composites ,Vanadate ,Physical and Theoretical Chemistry ,0210 nano-technology ,Stoichiometry ,Monoclinic crystal system - Abstract
Three new strontium manganese vanadates, Sr 2 Mn 2 (V 3 O 10 )(VO 4 ) ( I ), Sr 3 Mn(V 2 O 7 ) 2 ( II ), and Sr 2 Mn(VO 4 ) 2 (OH) ( III ), were prepared using a high temperature (580 °C) hydrothermal method with various chloride salts as the mineralizer. Minor differences in the chloride stoichiometry led to significant differences in product. Compound I crystallizes in the monoclinic space group P 2 1 / c ( a = 6.8773(12) A, b = 15.061(3) A, c = 11.609(2) A, β = 96.745(8)°), and consists of edge-shared octahedral manganese(II) dimers coordinated by trimeric [V 3 O 10 ] and monomeric [VO 4 ] groups. Compound II crystallizes in the tetragonal crystal system, P 4 3 2 1 2 ( a = 6.9951(2) A, c = 25.4390(7) A), and is built from monomeric manganese(II) octahedra chelated by two pyrovanadate [V 2 O 7 ] groups and linked to each other by additional pyrovanadates to form layers. Compound III is a noncentrosymmetric variation on the brackebuschite structure type, crystallizing in the monoclinic space group P 2 1 ( a = 7.6316(3) A, b = 6.1204(3) A, c = 8.6893(3) A, β = 111.3940(10)°). The structure is composed of octahedral manganese(III) edge-sharing chains coordinated to corner-sharing monomeric [VO 4 ] groups, thereby forming a manganese vanadate chain. All compounds were characterized by single-crystal X-Ray diffraction, powder X-Ray diffraction, infrared spectroscopy and single-crystal Raman spectroscopy. Density functional theory calculations were employed to investigate the relative stability of compound III .
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- 2017
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4. One-Pot Hydrothermal Synthesis of TbIII13(GeO4)6O7(OH) and K2TbIVGe2O7: Preparation of a Stable Terbium(4+) Complex
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Liurukara D. Sanjeewa, George Chumanov, Yimei Wen, Colin D. McMillen, Apeksha C. Rajamanthrilage, Jeffrey N. Anker, Kyle Fulle, and Joseph W. Kolis
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Inorganic chemistry ,Oxide ,Solid-state ,chemistry.chemical_element ,Terbium ,02 engineering and technology ,Trigonal crystal system ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,Crystallography ,chemistry ,Oxidation state ,Hydrothermal synthesis ,Physical and Theoretical Chemistry ,Isostructural ,0210 nano-technology - Abstract
Two terbium germanates have been synthesized via high-temperature and high-pressure hydrothermal synthesis with 20 M KOH as a mineralizer using Tb4O7 as a starting material. Tb13(GeO4)6O7(OH) crystallizes in trigonal space group R3, is built up of isolated GeO4 units, and contains a complex arrangement of terbium oxide polyhedra. K2TbGe2O7 is a terbium(4+) pyrogermanate that is isostructural with K2ZrGe2O7 and displays a rare stable Tb4+ oxidation state in the solid state.
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- 2017
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5. Synthesis and characterization of new fluoride-containing manganese vanadates A2Mn2V2O7F2 (A=Rb, Cs) and Mn2VO4F
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George Chumanov, Joseph W. Kolis, Liurukara D. Sanjeewa, Michael A. McGuire, Daniel Willett, Colin D. McMillen, Tiffany M. Smith Pellizzeri, and V. Ovidiu Garlea
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010405 organic chemistry ,Chemistry ,Infrared spectroscopy ,010402 general chemistry ,Condensed Matter Physics ,01 natural sciences ,Magnetic susceptibility ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Inorganic Chemistry ,symbols.namesake ,Crystallography ,Nuclear magnetic resonance ,Molecular vibration ,Materials Chemistry ,Ceramics and Composites ,symbols ,Antiferromagnetism ,Physical and Theoretical Chemistry ,Raman spectroscopy ,Single crystal ,Néel temperature ,Monoclinic crystal system - Abstract
Large single crystals of A2Mn2V2O7F2 (A=Rb, Cs) and Mn2VO4F were grown using a high-temperature (~600 °C) hydrothermal technique. Single crystal X-ray diffraction and powder X-ray diffraction were utilized to characterize the structures, which both possess MnO4F2 building blocks. The A2Mn2V2O7F2 series crystallizes as a new structure type in space group Pbcn (No. 60), Z=4 (Rb2Mn2V2O7F2: a=7.4389(17) A, b=11.574(3) A, c=10.914(2) A; Cs2Mn2V2O7F2: a=7.5615(15) A, b=11.745(2) A, c=11.127(2) A). The structure is composed of zigzag chains of edge-sharing MnO4F2 units running along the a-axis, and interconnected through V2O7 pyrovanadate groups. Temperature dependent magnetic susceptibility measurements on this interesting one-dimensional structural feature based on Mn2+ indicated that Cs2Mn2V2O7F2 is antiferromagnetic with a Neel temperature, TN=~3 K and a Weiss constant, θ, of −11.7(1) K. Raman and infrared spectra were also analyzed to identify the fundamental V–O vibrational modes in Cs2Mn2V2O7F2. Mn2(VO4)F crystalizes in the monoclinic space group of C2/c (no. 15), Z=8 with unit cell parameters of a=13.559(2) A, b=6.8036(7) A, c=10.1408(13) A and β=116.16(3)°. The structure is associated with those of triplite and wagnerite. Dynamic fluorine disorder gives rise to complex alternating chains of five-and six-coordinate Mn2+. These interpenetrating chains are additionally connected through isolated VO4 tetrahedra to form the condensed structure.
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- 2016
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6. Honeycomb-like S = 5/2 Spin–Lattices in Manganese(II) Vanadates
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George Chumanov, Liurukara D. Sanjeewa, Joseph W. Kolis, Colin D. McMillen, Daniel Willett, and Michael A. McGuire
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Chemistry ,chemistry.chemical_element ,02 engineering and technology ,Manganese ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Honeycomb like ,Hydrothermal circulation ,0104 chemical sciences ,Inorganic Chemistry ,Trigonal bipyramidal molecular geometry ,Crystallography ,Octahedron ,Vanadate ,Physical and Theoretical Chemistry ,0210 nano-technology - Abstract
New complex manganese vanadate materials were synthesized as high-quality single crystals in multi-millimeter lengths using a high-temperature, high-pressure hydrothermal method. One compound, Mn5(VO4)2(OH)4, was grown from Mn2O3 and V2O5 in 3 M CsOH at 580 °C and 1.5 kbar. Changing the mineralizer to 1 M CsOH/3MCsCl leads to the formation of another product, Mn6O(VO4)2(OH). Both compounds were structurally characterized by single-crystal X-ray diffraction (Mn5(VO4)2(OH)4: C2/m, Z = 2, a = 9.6568(9) Å, b = 9.5627(9) Å, c = 5.4139(6) Å, β = 98.529(8)°; Mn6O(VO4)2(OH): P21/m, Z = 2, a = 8.9363(12) Å, b = 6.4678(8) Å, c = 10.4478(13) Å, β = 99.798(3)°), revealing interesting low-dimensional transition-metal features. Mn5(VO4)2(OH)4 possesses complex honeycomb-type Mn-O layers, built from edge-sharing [MnO6] octahedra in the bc plane, with bridging vanadate groups connecting these layers along the a-axis. Mn6O(VO4)2(OH) presents a more complicated structure with both octahedral [MnO6] and trigonal bipyramidal [MnO5] units. A different pattern of planar honeycomb sheets are formed by edge-shared [MnO6] octahedra, and these sublattices are connected through edge-shared dimers of [MnO5] trigonal bipyramids to form corrugated sheets. Vanadate groups again condense the sheets into a three-dimensional framework. Infrared and Raman spectroscopies indicated the presence of OH groups and displayed characteristic Raman scattering due to vanadate groups. Temperature-dependent magnetic studies indicated Curie-Weiss behavior above 100 K with significant anti-ferromagnetic coupling for both compounds, with further complex magnetic behavior at lower temperatures. The data indicate canted anti-ferromagnetic order below 57 K in Mn5(VO4)2(OH)4 and below 45 K in Mn6O(VO4)2(OH). Members of another class of compounds, K2M3(VO4)2(OH)2 (M = Mn, Co), also containing a honeycomb-type sublattice, were also synthesized to allow a comparison of the structural features across all three structure types and to demonstrate extension to other transition metals.
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- 2016
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7. Hydrothermal synthesis of single crystals of transition metal vanadates in the glaserite phase
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Liurukara D. Sanjeewa, Daniel Willett, George Chumanov, Joseph W. Kolis, and Colin D. McMillen
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Materials science ,media_common.quotation_subject ,Neutron diffraction ,Frustration ,Crystal growth ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Hydrothermal circulation ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Inorganic Chemistry ,Crystallography ,Transition metal ,Materials Chemistry ,Ceramics and Composites ,Hydrothermal synthesis ,Vanadate ,Physical and Theoretical Chemistry ,0210 nano-technology ,Single crystal ,media_common - Abstract
A series of transition metal vanadate crystals were prepared using a high temperature (580 °C) hydrothermal method. The compounds all had the general formula A 2 AEM (VO 4 ) 2 ( A =K, Na, Li; AE =Ba, Sr; M =Co, Fe, Mn). They are all variations of the glaserite structural type and range in symmetry from P- 3 m 1 to P -3 to P 2 1 / c . Most of the derivatives contain a planar three-fold rotation operation, making them possible spin frustration candidates. Single crystal structural analyses were performed on many of the derivatives to obtain a detailed understanding of the distortions of the tetrahedral building blocks that accommodate the symmetry distortions. A hydrothermal growth method was developed to grow high quality single crystals of sizes up to 2–3 mm/edge. This method can be generalized for large crystal growth to enable magnetic and neutron diffraction studies that require relatively large single crystals.
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- 2016
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8. Hydrothermal Synthesis and Characterization of Novel Brackebuschite-Type Transition Metal Vanadates: Ba2M(VO4)2(OH), M = V3+, Mn3+, and Fe3+, with Interesting Jahn–Teller and Spin-Liquid Behavior
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Longyu Hu, Liurukara D. Sanjeewa, Colin D. McMillen, George Chumanov, Michael A. McGuire, Joseph W. Kolis, and Vasile O. Garlea
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Chemistry ,Jahn–Teller effect ,Inorganic chemistry ,Infrared spectroscopy ,Inorganic Chemistry ,Crystallography ,symbols.namesake ,Transition metal ,Octahedron ,symbols ,Hydrothermal synthesis ,Vanadate ,Physical and Theoretical Chemistry ,Raman spectroscopy ,Monoclinic crystal system - Abstract
A new series of transition metal vanadates, namely, Ba2M(VO4)2(OH) (M = V(3+), Mn(3+), and Fe(3+)), was synthesized as large single crystals hydrothermally in 5 M NaOH solution at 580 °C and 1 kbar. This new series of compounds is structurally reminiscent of the brackebuschite mineral type. The structure of Ba2V(VO4)2(OH) is monoclinic in space group P21/m, a = 7.8783(2) Å, b = 6.1369(1) Å, c = 9.1836(2) Å, β = 113.07(3)°, V = 408.51(2) Å(3). The other structures are similar and consist of one-dimensional trans edge-shared distorted octahedral chains running along the b-axis. The vanadate groups bridge across edges of their tetrahedra. Structural analysis of the Ba2Mn(VO4)2(OH) analogue yielded a new understanding of the Jahn-Teller effect in this structure type. Raman and infrared spectra were investigated to observe the fundamental vanadate and hydroxide vibrational modes. Single-crystal temperature-dependent magnetic studies on Ba2V(VO4)2(OH) reveal a broad feature over a wide temperature range with maximum at ∼100 K indicating that an energy gap could exist between the antiferromagnetic singlet ground state and excited triplet states, making it potentially of interest for quantum magnetism studies.
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- 2015
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9. Three Unique Barium Manganese Vanadates from High-Temperature Hydrothermal Brines
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Joseph W. Kolis, Yimei Wen, Tiffany M. Smith Pellizzeri, Colin D. McMillen, and George Chumanov
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010405 organic chemistry ,Hexagonal crystal system ,Barium chloride ,Inorganic chemistry ,chemistry.chemical_element ,Barium ,Manganese ,010402 general chemistry ,01 natural sciences ,Hydrothermal circulation ,0104 chemical sciences ,Inorganic Chemistry ,Crystallography ,chemistry.chemical_compound ,chemistry ,Octahedron ,Orthorhombic crystal system ,Physical and Theoretical Chemistry - Abstract
Three new barium manganese vanadates, all containing hexagonal barium chloride layers interpenetrated by [V2O7]4– groups, were synthesized using a high-temperature (580 °C) hydrothermal method. Two of the compounds were prepared from a mixed BaCl2/Ba(OH)2 mineralizer, and the third compound was prepared from BaCl2 mineralizer. An interesting structural similarity exists between two of the compounds, Ba2Mn(V2O7)(OH)Cl and Ba4Mn2(V2O7)(VO4)2O(OH)Cl. These two compounds crystallize in the orthorhombic space group Pnma, Z = 4, and are structurally related by a nearly doubled a axis. The first structure, Ba2Mn(V2O7)(OH)Cl (I) (a = 15.097(3) A, b = 6.1087(12) A, c = 9.5599(19) A), consists of octahedral manganese(II) edge-sharing chains linked by pyrovanadate [V2O7] groups, generating a three-dimensional structure. Compound II, Ba4Mn2(V2O7)(VO4)2O(OH)Cl (a = 29.0814(11) A, b = 6.2089(2) A, c = 9.5219(4) A), is composed of manganese(III) edge-sharing chains that are coordinated to one another through pyrovanadat...
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- 2017
10. Tuning Localized Surface Plasmon Resonance Wavelengths of Silver Nanoparticles by Mechanical Deformation
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Shilpa Varahagiri, Yimei Wen, Fathima S. Ameer, Jeffrey N. Anker, George Chumanov, Daniel Willett, Donald Benza, and Fenglin Wang
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Materials science ,Scanning electron microscope ,Scattering ,Physics::Optics ,Nanoparticle ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Silver nanoparticle ,Article ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,symbols.namesake ,General Energy ,Nano ,symbols ,Physical and Theoretical Chemistry ,Surface plasmon resonance ,0210 nano-technology ,Raman spectroscopy ,Spectroscopy - Abstract
We describe a simple technique to alter the shape of silver nanoparticles (AgNPs) by rolling a glass tube over them to mechanically compress them. The resulting shape change in turn induces a red-shift in the localized surface plasmon resonance (LSPR) scattering spectrum and exposes new surface area. The flattened particles were characterized by optical and electron microscopy, single nanoparticle scattering spectroscopy, and surface enhanced Raman spectroscopy (SERS). AFM and SEM images show that the AgNPs deform into discs; increasing the applied load from 0 to 100 N increases the AgNP diameter and decreases the height. This deformation caused a dramatic red shift in the nanoparticle scattering spectrum and also generated new surface area to which thiolated molecules could attach as evident from SERS measurements. The simple technique employed here requires no lithographic templates and has potential for rapid, reproducible, inexpensive and scalable tuning of nanoparticle shape, surface area, and resonance while preserving particle volume.
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- 2017
11. Depolarized Light Scattering From Single Silver Nanoparticles
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George Chumanov and John C. Heckel
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Brewster's angle ,business.industry ,Scattering ,Chemistry ,Scanning electron microscope ,Physics::Optics ,Nanoparticle ,Polarization (waves) ,Molecular physics ,Silver nanoparticle ,Light scattering ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,symbols.namesake ,General Energy ,Optics ,symbols ,Physical and Theoretical Chemistry ,business ,Plasmon - Abstract
Depolarized scattering spectra from individual silver nanoparticles of different shapes and sizes were measured as a function of the incident polarization angle. The spectra were correlated to the nanoparticles’ shape, size, and orientation as determined by scanning electron microscopy. The intensity of depolarized scattered light from nonspherical silver nanoparticles strongly depends upon particle shape and orientation relative to the polarization vector. The intensity of depolarized scattered light also increases with the aspect ratio of the nanoparticles. The depolarized light scattering originated from the interference of the plasmon modes corresponding to the electron oscillations along different axes of the NPs.
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- 2011
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12. Plasmon Coupling in Two-Dimensional Arrays of Silver Nanoparticles: I. Effect of the Dielectric Medium
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Svetlana Kachan, George Chumanov, Mark K. Kinnan, and Courtenay K. Simmons
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Materials science ,business.industry ,Surface plasmon ,Physics::Optics ,Dielectric ,Surface plasmon polariton ,Molecular physics ,Silver nanoparticle ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Materials Science ,General Energy ,Adsorption ,Optics ,Extinction (optical mineralogy) ,Physics::Atomic and Molecular Clusters ,Physical and Theoretical Chemistry ,business ,Refractive index ,Localized surface plasmon - Abstract
The effect of the dielectric medium between the particles on plasmon coupling was studied experimentally and theoretically. Two-dimensional arrays of silver nanoparticles adsorbed on glass slides were immobilized using poly(methylmethacrylate). The method provides an efficient way for stabilization of particles on surfaces. It was concluded that increasing the dielectric function of the surrounding medium promotes plasmon coupling between silver nanoparticles. On the basis of the quasi-crystalline approximation, the optimum refractive index was calculated that yielded the strongest and highest Q extinction band due to coherent plasmon coupling.
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- 2009
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13. Surface Enhanced Raman Scattering and Resonance Elastic Scattering from Capped Single Ag Nanoparticles
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Stephen D. Hudson and George Chumanov
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Elastic scattering ,Materials science ,business.industry ,Physics::Optics ,Nanoprobe ,Nanoparticle ,Photochemistry ,Resonance (particle physics) ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,symbols.namesake ,General Energy ,Optics ,Physics::Atomic and Molecular Clusters ,symbols ,Particle ,Physical and Theoretical Chemistry ,business ,Anisotropy ,Raman spectroscopy ,Raman scattering - Abstract
Capped Ag nanoparticles with the novel silver core−molecule−silver cap structure were synthesized and demonstrated to produce strong SERS. Plasmon-induced electronic coupling was concluded to be the major Raman enhancement mechanism. The capped nanoparticles also exhibited polarization-dependent elastic light scattering that was attributed to the particle anisotropy, which resulted from the addition of the silver cap. These particles can potentially be used as optical labels.
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- 2008
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14. The effect of fructose derived carbon shells on the plasmon resonance and stability of silver nanoparticles
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John C. Heckel, Fatimah F. Farhan, and George Chumanov
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Materials science ,Polymers and Plastics ,Inorganic chemistry ,Nanoparticle ,chemistry.chemical_element ,Silver nanoparticle ,Colloid and Surface Chemistry ,chemistry ,Ionic strength ,Materials Chemistry ,Hydrothermal synthesis ,Particle size ,Physical and Theoretical Chemistry ,Surface plasmon resonance ,Carbon ,Plasmon - Abstract
Carbon nanoparticles between 10 and 50 nm in diameter and carbon shells of various thickness around silver nanoparticles were synthesized by the hydrothermal reaction of fructose. The effect of the carbon shells on the plasmon resonance of the silver nanoparticles and their stability in sodium chloride solutions was investigated. The shell thickness can be adjusted to have insignificant damping of the plasmon resonance and provide stabilization of the particles in solutions with high ionic strength. Hydrazine–carbonyl cross-linking reactions were performed to link fluorescent dye molecules to carbonyl groups on the carbon shell surface.
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- 2008
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15. Surface Enhanced Raman Scattering from Silver Nanoparticle Arrays on Silver Mirror Films: Plasmon-Induced Electronic Coupling as the Enhancement Mechanism
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Mark K. Kinnan and and George Chumanov
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Materials science ,Nanoprobe ,Nanotechnology ,Silver nanoparticle ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Metal ,symbols.namesake ,General Energy ,Adsorption ,Chemical physics ,visual_art ,visual_art.visual_art_medium ,symbols ,Molecule ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Raman spectroscopy ,Plasmon ,Raman scattering - Abstract
Analysis of surface enhanced Raman scattering spectra from 20 different molecules adsorbed on substrates composed of silver nanoparticles immobilized on silver mirror films revealed competitive Raman enhancement from different types of molecules simultaneously present on the surface. The observed SERS behavior could not be explained using local field enhancement or charge-transfer models. A different SERS mechanism is proposed based on plasmon-induced electronic coupling between the oscillating electrons in the metal and the electronic system of adsorbed molecules. It is suggested that this mechanism has general applicability to other SERS-exhibiting systems.
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- 2007
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16. Synthesis of core-shell silver colloidal particles by surface immobilization of an azo-initiator
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Stephen H. Foulger, George Chumanov, David L. Carroll, Hua Bao, and Richard Czerw
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Materials science ,Polymers and Plastics ,Nanoparticle ,Silver nanoparticle ,Colloid and Surface Chemistry ,Adsorption ,Chemical engineering ,Dynamic light scattering ,Polymerization ,Particle-size distribution ,Polymer chemistry ,Materials Chemistry ,Physical and Theoretical Chemistry ,Fourier transform infrared spectroscopy ,Layer (electronics) - Abstract
Silver nanoparticles, with the diameter of approximately 100 nm, were coated with a 5–10 nm layer of poly(styrene-co-4-styrenesulfonic acid sodium salt). Polymerization was initiated on the particles by a surface adsorbed 4,4′-azobis(4-cyanovaleric acid) initiator. FTIR, electron microscopy, dynamic light scattering, and optical spectroscopy were employed to differentiate between the original and coated particles.
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- 2004
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17. Size-Controlled Synthesis of Nanoparticles. 2. Measurement of Extinction, Scattering, and Absorption Cross Sections
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David D. Evanoff and George Chumanov
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Cross section (physics) ,Chemistry ,Extinction (optical mineralogy) ,Scattering ,Materials Chemistry ,Absorption cross section ,Analytical chemistry ,Particle ,Physical and Theoretical Chemistry ,Surface plasmon resonance ,Absorption (electromagnetic radiation) ,Silver nanoparticle ,Surfaces, Coatings and Films - Abstract
Extinction, scattering, and absorption cross sections and efficiencies were experimentally measured for chemically clean silver nanoparticles in water for 16 different sizes ranging from 29 to 136 nm. The measured efficiencies indicate that particles interact with light 4-10 times stronger than the geometric cross section suggests. Absorption and scattering components of the plasmon resonance were separately measured across the visible spectral range. A method, termed standard subtraction, is suggested for the simple and reliable determination of particle concentrations independent of their size, shape, and aggregation state.
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- 2004
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18. Size-Controlled Synthesis of Nanoparticles. 1. 'Silver-Only' Aqueous Suspensions via Hydrogen Reduction
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Jr. and David D. Evanoff and George Chumanov
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Materials science ,Aqueous solution ,Hydrogen ,Oxide ,chemistry.chemical_element ,Nanoparticle ,Nanotechnology ,Silver nanoparticle ,Surfaces, Coatings and Films ,law.invention ,Metal ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,law ,visual_art ,Materials Chemistry ,visual_art.visual_art_medium ,Physical and Theoretical Chemistry ,Spectroscopy ,Filtration - Abstract
A method for size-controlled synthesis of chemically clean silver nanoparticles is proposed and described. The synthesis is based on the reduction of silver(I) oxide by hydrogen gas in water and offers the advantages of being easily scalable and able to produce essentially naked particles still exhibiting long-term stability with the metal surface readily accessible to various chemical modifications. The method allows synthesis of particles of any diameter between 15 and 200 nm simply by varying the reaction time. The addition of filtration and centrifugation techniques produces suspensions of narrow size distribution and relatively high, 1012−1014 particles/mL, concentration. The addition of various complexating agents potentially allows control of nanoparticle shape. The nanoparticles were characterized by UV−vis spectroscopy, electron microscopy, and electron and X-ray diffraction techniques.
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- 2004
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19. Poly(Vinyl Pyridine) as a Universal Surface Modifier for Immobilization of Nanoparticles
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Serhiy Z. Malynych, and Igor Luzinov, and George Chumanov
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chemistry.chemical_classification ,Materials science ,Absorption spectroscopy ,Oxide ,Nanoparticle ,Polymer ,Dielectric ,Surfaces, Coatings and Films ,Metal ,chemistry.chemical_compound ,Adsorption ,chemistry ,Chemical engineering ,visual_art ,Polymer chemistry ,Materials Chemistry ,visual_art.visual_art_medium ,Surface modification ,Physical and Theoretical Chemistry - Abstract
Metal, metal oxide, and plastic surfaces were modified with poly(vinylpyridine) using adsorption, spin-coating, and dip-coating techniques and various metal, semiconductor, and dielectric nanoparticles were subsequently attached. Prior to the modification, the substrates were treated with glow discharge plasma for cleaning purposes and to introduce surface functional groups that are capable of interaction with the polymer. UV−vis absorption spectroscopy, atomic force, and electron scanning microscopies were used to characterize polymer layers and layers of immobilized nanoparticles. The surface modification with poly(vinylpyridine) via adsorption technique is suggested as a simple, effective, and highly versatile method for the preparation of single, mixed, and multilayered assemblies of various nanoparticles on different substrates.
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- 2002
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20. Photoinduced electron transfer at the surface of nanosized silver particles as monitored by EPR spectroscopy
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George Chumanov, Therese M. Cotton, and Junwei Zheng
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Inorganic chemistry ,General Physics and Astronomy ,Nanoparticle ,Photochemistry ,Silver nanoparticle ,Photoinduced electron transfer ,law.invention ,Nitrophenol ,chemistry.chemical_compound ,Colloid ,Electron transfer ,chemistry ,law ,Physical and Theoretical Chemistry ,Surface plasmon resonance ,Electron paramagnetic resonance - Abstract
EPR spectroscopy was employed in study of photoinduced electron transfer on nanosized silver particles. Radicals were observed for the silver colloid with methylviologen (MV), nitrophenol and methanol with irradiation of UV lights. The wavelength dependence of EPR spectra of silver colloid with methanol indicates that plasmon resonance may be critical for the formation of the radicals on the nanosized silver particles.
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- 2001
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21. Multidimensional Reaction Coordinate for the Excited-state H-atom Transfer in Perylene Quinones: Importance of the 7-Membered Ring in Hypocrellins A and B
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Anindya Datta, Jacob W. Petrich, George Chumanov, Jin Wen, and Alexandre V. Smirnov
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Photosensitizing Agents ,Molecular Structure ,Phenol ,Photochemistry ,Chemistry ,Quinones ,General Medicine ,Ring (chemistry) ,Biochemistry ,Fluorescence ,Photon upconversion ,Reaction coordinate ,Kinetics ,chemistry.chemical_compound ,Spectrophotometry ,Excited state ,Intramolecular force ,Ultrafast laser spectroscopy ,Solvents ,Physical and Theoretical Chemistry ,Perylene - Abstract
The excited-state intramolecular H-atom transfer reactions of hypocrellins B and A are compared by using time-resolved absorption and fluorescence upconversion techniques. The hypocrellin B photophysics are well described by a simple model involving one ground-state species and excited-state forward and reverse H-atom transfer with a nonfluorescent excited state. We suggest that excited-state conformational changes are coupled to the H-atom transfer in hypocrellin B just as gauche/anti changes are coupled to the H-atom transfer in hypocrellin A.
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- 2000
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22. Photoinduced Electrochemical Reduction of Nitrite at an Electrochemically Roughened Silver Surface
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Therese M. Cotton, Tianhong Lu, George Chumanov, and Junwei Zheng
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Photocurrent ,chemistry.chemical_classification ,Chemistry ,Inorganic chemistry ,Electron acceptor ,Electrochemistry ,Photochemistry ,Surfaces, Coatings and Films ,Metal ,chemistry.chemical_compound ,Ammonia ,Nitrate ,visual_art ,Materials Chemistry ,visual_art.visual_art_medium ,Physical and Theoretical Chemistry ,Nitrite ,Plasmon - Abstract
Photoelectrochemical reduction of nitrite and nitrate was studied on the surface of an electrochemically roughened silver electrode. The dependence of the photocurrent on photon energy, applied potential, and concentration of nitrite was determined. It was concluded that the photoelectrochemical reduction proceeds via a photoemission process followed by the capture of hydrated electrons by electron acceptors. The excitation of plasmon resonances in nanosize metal structures produced during the roughening procedure resulted in the enhancement of the photoemission process. Ammonia was detected as one of the final products in this reaction. Mechanisms for the photoelectrochemical reduction of nitrite and nitrate are proposed.
- Published
- 1999
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23. Low-Temperature Resonance Raman Scattering from Iodide Adsorbed on Nanostructured Silver Surfaces
- Author
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and Morgan S. Sibbald, George Chumanov, and Therese M. Cotton
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chemistry.chemical_classification ,Materials science ,Overtone ,Iodide ,Analytical chemistry ,Resonance ,Supermolecule ,Surfaces, Coatings and Films ,symbols.namesake ,chemistry ,Normal mode ,Excited state ,Materials Chemistry ,symbols ,Physical and Theoretical Chemistry ,Raman spectroscopy ,Raman scattering - Abstract
An overtone progression was observed in Raman scattering spectra from iodide-modified, electrochemically roughened silver surfaces at low temperatures. Spectral intensities of the bands were found to vary with the degree of surface roughening, whereas vibrational frequencies remained highly conserved. Both surface-enhanced and resonance scattering phenomena contribute to observed band intensities when excited in the spectral region between 406 and 415 nm. It is suggested that the progression originates from I2-like species that are formed on small silver clusters at low temperatures under irradiation. This complex can be viewed as a supermolecule in which the electronic resonance is determined by the size of the cluster and I−I stretch represents a normal mode of the molecule.
- Published
- 1998
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24. Multiple-overtone resonance Raman scattering and fluorescence from I2 species adsorbed on silver surfaces
- Author
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Gerald J. Small, Therese M. Cotton, George Chumanov, and Morgan S. Sibbald
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Chemistry ,Overtone ,General Physics and Astronomy ,Resonance ,Spectral line ,symbols.namesake ,Excited state ,symbols ,Physical and Theoretical Chemistry ,Atomic physics ,Ground state ,Raman spectroscopy ,Excitation ,Raman scattering - Abstract
A detailed excitation profile of a Raman progression consisting of up to six overtones and a fundamental band at 123 cm−1 observed from iodide adsorbed on an electrochemically roughened silver surface at 20 K is analyzed. The excitation profile was constructed from 77 spectra obtained by tuning the laser wavelength in ∼0.25 nm steps through the spectral range 409 nm–433 nm. The shift between resonances in the excitation profile, corresponding to the spacing between vibronic levels in the excited state, is also equal to 123 cm−1 indicating that the ground state and excited state potential energy surfaces have the same shape. Only two distinct resonances spaced three vibrational quanta apart were evident in the profile for each band in the progression. Curve fitting of the Raman band shapes indicates that each overtone is composed of one sharp and one broad band, whereas the fundamental contains only one sharp component. The measured width of the fundamental was less than 2.5 cm−1 FWHM, limited by the instr...
- Published
- 1998
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25. Resonance Raman study of carotenoid cation radicals
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Lowell D. Kispert, Chengli Zhou, Antony S. Jeevarajan, Therese M. Cotton, and George Chumanov
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Chemistry ,Radical ,General Physics and Astronomy ,Photochemistry ,Resonance (chemistry) ,Spectral line ,law.invention ,Delocalized electron ,symbols.namesake ,Unpaired electron ,law ,symbols ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,Raman spectroscopy ,Excitation - Abstract
The resonance Raman (RR) spectra of the neutral and the cation radical of 8′-apo-β-caroten-8′-al (I), 7′,7′-dicyano-7′-apo-β-carotene (II) and canthaxanthin (III) were measured using 752.6 nm laser excitation. Optical and RR spectra of the electrochemically prepared cation radicals of I–III were measured in situ at different time intervals during the electrolysis. The RR spectra of the cation radicals are considerably different from those of the neutral species. The frequencies of the CC stretching vibrations are decreased by 30–40 cm −1 , whereas those of CC stretching vibrations are increased by 15–30 cm −1 . These results suggest delocalization of the unpaired electron density throughout the entire carbon backbone which is consistent with our previous EPR and ENDOR results.
- Published
- 1996
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26. Photoreduction of Methylviologen Adsorbed on Silver
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George Chumanov, Therese M. Cotton, and Hannah Feilchenfeld
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Chemistry ,General Engineering ,Liquid nitrogen ,Photochemistry ,Dication ,Electrochemical cell ,symbols.namesake ,Electron transfer ,Electrode ,symbols ,Irradiation ,Physical and Theoretical Chemistry ,Raman spectroscopy ,Raman scattering - Abstract
Methylviologen adsorbed on a roughened silver electrode is reduced to its cation radical upon irradiation with laser light at liquid nitrogen temperature. Surface-enhanced Raman scattering (SERS) spectra were obtained with different excitation wavelengths between 406 and 752 nm and compared to those obtained at room temperature in an electrochemical cell under potential control. From two-color experiments, in which one laser frequency was used to generate the radical and a second to excite the SERS spectra, it was determined that radical formation occurs mainly with excitation in the blue spectral region. A comparison of the SERS spectra of the dication and cation radical forms of methylviologen with their solution spectra suggests that the former interacts more strongly with the surface than the latter. The cation radical appears to be stable for several hours in liquid nitrogen but has a short lifetime at room temperature. Two mechanisms for the photoreduction are discussed: plasmon-assisted electron t...
- Published
- 1996
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27. Reduction of Cytochrome c by Halide-Modified, Laser-Ablated Silver Colloids
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Morgan S. Sibbald, Therese M. Cotton, and and George Chumanov
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endocrine system ,Laser ablation ,Chemistry ,digestive, oral, and skin physiology ,General Engineering ,Analytical chemistry ,Resonance ,Halide ,complex mixtures ,body regions ,Colloid ,Adsorption ,Particle ,Physical and Theoretical Chemistry ,Absorption (chemistry) ,Surface plasmon resonance - Abstract
Silver colloids of 20 nm mean particle diameter were prepared by laser ablation and modified by adsorption of iodide and bromide ions. Addition of cytochrome c to this colloid resulted in the reduction of the protein, which was monitored by surface-enhanced resonance Raman scattering and absorption spectroscopies. Colloidal metal films, prepared from the same Ag colloid, were employed to minimize contributions from aggregation. Effects of surface modification on the Ag plasmon resonance were studied in both colloidal suspensions and colloidal metal films. The conclusion was made that adsorption of I- and Br- results in charging of the Ag particle as a whole and a shift of its potential to more negative values. The donated charge is delocalized in a thin surface layer and does not significantly affect the plasmon resonance frequency of the particle.
- Published
- 1996
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28. Measuring the Distance Dependence of the Local Electromagnetic Field from Silver Nanoparticles
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George Chumanov, Ryan L. White, and David D. Evanoff
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Electromagnetic field ,Materials science ,Condensed matter physics ,business.industry ,Physics::Optics ,Dielectric ,Electron ,engineering.material ,Silver nanoparticle ,Surfaces, Coatings and Films ,Optics ,Coating ,Materials Chemistry ,engineering ,Particle ,Physical and Theoretical Chemistry ,Surface plasmon resonance ,business ,Silver particles - Abstract
The distance dependence of the local EM field associated with 84 ± 5 nm silver particles is characterized by monitoring spectral shifts in the plasmon resonance due to changes in local dielectric environment, which was controlled by coating the particles with silica layers of various thicknesses. The local EM field that extends beyond the physical boundaries of the particles is defined as that providing “feedback” between the local environment and the electron oscillations in a particle.
- Published
- 2004
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29. Colloidal metal films as a substrate for surface-enhanced spectroscopy
- Author
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Brian W. Gregory, Therese M. Cotton, George Chumanov, and Konstantin V Sokolov
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Chemistry ,General Engineering ,Analytical chemistry ,Substrate (electronics) ,Dielectric ,Metal ,symbols.namesake ,Colloid ,Adsorption ,Chemical engineering ,visual_art ,visual_art.visual_art_medium ,symbols ,Physical and Theoretical Chemistry ,Spectroscopy ,Plasmon ,Raman scattering - Abstract
Colloidal films of gold and silver were prepared on glass or quartz slides. The slides were derivatized with (3-mercaptopropyl)trimethoxysilane and subsequently reacted with aqueous metal colloids for variable time periods. The formation of the sulfur-metal bond provides a stable colloidal film on the surface. Because of the electrostatic interaction between individual particles, a semiregular structure is produced, as can be seen from electron micrographs. The unique property of the colloidal film is that they possess the optical properties of colloidal metals and the convenience of solid substrates. The effect of the dielectric constant of solvents on the optical frequencies, as well as the specific interaction of the solvent molecules with the metal on the plasmon resonances, was examined in detail. The colloidal films exhibit strong enhancement of Raman scattering and fluorescence emission from molecules adsorbed on the surface. Enhancement of fluorescence was observed for fluorescein-labeled molecules spaced 0-200 A away from the surface. These substrates can be used in a number of analytical applications, such as surface-enhanced spectroscopies as well as for fundamental studies of plasmon resonances in small metal particles. 40 refs., 6 figs., 1 tab.
- Published
- 1995
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30. Surface-Enhanced Resonance Raman Scattering Spectroscopy of Photosystem II Pigment-Protein Complexes
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Michael Seibert, Rafael Picorel, Therese M. Cotton, Stephen Toon, George Chumanov, and Guillermo Montoya
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Photosystem II ,General Engineering ,food and beverages ,Photochemistry ,Resonance (chemistry) ,Sodium dithionite ,symbols.namesake ,chemistry.chemical_compound ,chemistry ,symbols ,Molecule ,Physical and Theoretical Chemistry ,Spectroscopy ,Raman spectroscopy ,Heme ,Raman scattering - Abstract
Three different photosystem II (PSII) pigment-protein complexes (D1-D2-Cyt b559-CP47, D1-D2-Cyt b559, and CP47) isolated from spinach were studied by surface-enhanced resonance Raman scattering (SERRS) spectroscopy. Surface-enhanced Raman scattering (SERS) is a distance sensitive (on a 5-10-Å scale) spectroscopic tool that can be used to examine structural properties of large biological molecules. It is demonstrated here that SERS can also be used to determine organizational relationships between different pigment-protein complexes. Strong SERRS spectra from the above PSII complexes before and after treatment with sodium dithionite were obtained on roughened Ag electrodes and in citrate-reduced Ag colloids. The D1-D2-Cyt b559 complex adsorbs with the Cyt b559 heme close to the surface in the colloid, whereas the complex adsorbs differently on the Ag electrode due to the differing surface properties of the two types of substrates. An analysis of the SERRS spectra led to the following conclusions: CP47 binds next to Cyt b559 in the D1-D2-Cyt b559-CP47 complex and covers the heme, the Cyt b559 heme is located closer to one side of the complex (the stromal side in the intact thylakoid membrane), and both Chl and β-carotene molecules are located closer to the opposite side of the complex. Assuming a barrel-shape structure for the pigment-protein complexes, the results imply that the complexes are oriented with the central axis perpendicular to the metal surface both in the colloids and on the electrodes. © 1994 American Chemical Society.
- Published
- 1994
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31. STRUCTURAL AND FUNCTIONAL INTEGRITY OF THE PHOTOSYSTEM II REACTION CENTER ON SILVER ELECTRODES: FLUORESCENCE AND REDOX PROBES
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George Chumanov, Stephen Toon, Rafael Picorel, Therese M. Cotton, and Michael Seibert
- Subjects
Photosynthetic reaction centre ,Photosystem II ,Chemistry ,Cytochrome b559 ,General Medicine ,Photochemistry ,Resonance (chemistry) ,Biochemistry ,Fluorescence ,Redox ,symbols.namesake ,Electrode ,symbols ,Physical and Theoretical Chemistry ,Raman scattering - Abstract
4 Pags., Two simple and sensitive methods have been developed to assess the structural and functional integrity of isolated photosystem II reaction centers deposited on a roughened Ag electrode. Surface-enhanced resonance Raman scattering (SERRS) spectra useful for ascertaining structural information can be obtained from biological materials with this technique. The first method presented is based on observing differences in the fluorescence emission properties of reaction centers; these depend on the activity of the material. The second is based on the observation of changes in Raman bands that are sensitive to the redox state of cytochrome b559 present in the reaction center complex. It is concluded that the conditions used here to obtain SERRS spectra do not affect the structural or functional integrity of the isolated photosystem II reaction center complex. In principle these approaches also could be used with other chromoproteins.
- Published
- 1993
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32. Nanoparticle-mirror sandwich substrates for surface-enhanced Raman scattering
- Author
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George Chumanov and Jacquitta K. Daniels
- Subjects
Materials science ,business.industry ,technology, industry, and agriculture ,Analytical chemistry ,Physics::Optics ,Nanoparticle ,Nanoprobe ,Charge-transfer complex ,Dipicolinic acid ,Silver nanoparticle ,Surfaces, Coatings and Films ,symbols.namesake ,chemistry.chemical_compound ,chemistry ,Physics::Atomic and Molecular Clusters ,Materials Chemistry ,symbols ,Optoelectronics ,Physical and Theoretical Chemistry ,business ,Raman spectroscopy ,Plasmon ,Raman scattering - Abstract
Sandwich surface-enhanced Raman scattering (SERS) substrates (3S) utilizing coupling between continuous metal films and plasmonic particles were fabricated using silver mirrors, electrochemically roughened films, and various sizes of silver nanoparticles. The effect of excitation wavelength and nanoparticle size on SERS spectra of poly(vinylpyridine), selected as a model compound, was studied to determine the optimum conditions for the strongest SERS signal. The Raman enhancement resulted from the plasmon coupling of silver nanoparticles to the underlying continuous film as well as the lateral plasmon coupling between the silver nanoparticles. The formation of the charge transfer complex was also observed. The 3S configuration was used to obtain SERS spectra of dipicolinic acid (DPA), a chemical signature for Bacillus anthracis.
- Published
- 2006
33. Synthesis and optical properties of silver nanoparticles and arrays
- Author
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George Chumanov and David D. Evanoff
- Subjects
Optics and Photonics ,Materials science ,Nanocomposite ,Silver ,Scattering ,Physics::Optics ,Nanoparticle ,Nanotechnology ,Surface Plasmon Resonance ,Sensitivity and Specificity ,Atomic and Molecular Physics, and Optics ,Silver nanoparticle ,Particle ,Nanoparticles ,Particle size ,Physical and Theoretical Chemistry ,Surface plasmon resonance ,Particle Size ,Crystallization ,Plasmon - Abstract
This Minireview systematically examines optical properties of silver nanoparticles as a function of size. Extinction, scattering, and absorption cross-sections and distance dependence of the local electromagnetic field, as well as the quadrupolar coupling of 2D assemblies of such particles are experimentally measured for a wide range of particle sizes. Such measurements were possible because of the development of a novel synthetic method for the size-controlled synthesis of chemically clean, highly crystalline silver nanoparticles of narrow size distribution. The method and its unique advantages are compared to other methods for synthesis of metal nanoparticles. Synthesis and properties of nanocomposite materials using these and other nanoparticles are also described. Important highlights in the history of the field of metal nanoparticles as well as an examination of the basic principles of plasmon resonances are included.
- Published
- 2005
34. Unusual Extinction Spectra of Nanometer-Sized Silver Particles Arranged in Two-Dimensional Arrays
- Author
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George Chumanov, Konstantin V Sokolov, and Therese M. Cotton
- Subjects
Condensed Matter::Soft Condensed Matter ,Colloid ,Chemistry ,General Engineering ,Analytical chemistry ,Resonance ,Nanometre ,Irradiation ,Physical and Theoretical Chemistry ,Thin film ,Surface plasmon resonance ,Plasmon ,Blueshift - Abstract
Two-dimensional arrays of 1000 A silver particles were prepared by adsorption from colloidal suspensions onto glass slides derivatized with (3-mercaptopropyl)trimethoxysilane. By variation of the concentration of the colloidal suspensions, slides with different interparticle distances were obtained, and their extinction spectra were measured in water. A blue shift (up to 90 nm) and sharpening of the peak corresponding to the plasmon resonance was observed as the distance between particles decreased to a value comparable to, or less than, their diameter. The angular dependence of the extinction spectra was studied for s- and p-polarized light. The data are interpreted to result from coherent coupling of the plasmon resonances in closely spaced silver particles upon irradiation with light.
- Published
- 1996
- Full Text
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35. Surface-enhanced resonance Raman scattering spectroscopy of plant photosystem II reaction centers excited on the red-edge of the Qy band
- Author
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Michael Seibert, Rafael Picorel, Elena Torrado, George Chumanov, and Therese M. Cotton
- Subjects
Photosynthetic reaction centre ,Quantitative Biology::Biomolecules ,Physics::Biological Physics ,P700 ,Materials science ,Photosystem II ,Red edge ,Resonance ,Photochemistry ,Surfaces, Coatings and Films ,symbols.namesake ,Excited state ,Materials Chemistry ,symbols ,Physical and Theoretical Chemistry ,Spectroscopy ,Raman scattering - Abstract
Using surface-enhanced resonance Raman scattering (SERRS) spectroscopy techniques, we have obtained vibrational spectra from the higher plant D1-D2-cytochrome b559 photosystem II reaction center complex by exciting directly into the red-edge of the Qy transitions of chlorophyll and pheophytin bound within the protein complex. The presence of the SERRS-active metallic Ag surface dramatically reduced the high fluorescence yield from these pigments, a serious problem that has prevented detection of resonance Raman scattering signals in the past. This report constitutes the first successful attempt to measure Raman spectra from an oxygenic photosynthetic pigment-protein complex by excitation within the Qy transition. Consequently, SERRS spectroscopy now shows promise as an alternative vibrational spectroscopy to FT-IR for selectively examining energy transfer and redox-active chromophores involved in the dynamics of the primary processes of photosynthesis.
- Published
- 1998
36. Resonance Raman and Surface-Enhanced Resonance Raman Spectra of LH2 Antenna Complex from Rhodobacter sphaeroides and Ectothiorhodospira sp. Excited in the Qx and Qy Transitions†
- Author
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George Chumanov, Therese M. Cotton, Rafael Picorel, Iñaki Ortiz de Zarate, and Michael Seibert
- Subjects
Ectothiorhodospira ,biology ,Chemistry ,Resonance ,General Medicine ,biology.organism_classification ,Photochemistry ,Biochemistry ,Rhodobacter sphaeroides ,symbols.namesake ,chemistry.chemical_compound ,Excited state ,symbols ,Photosynthetic bacteria ,Bacteriochlorophyll ,Physical and Theoretical Chemistry ,Raman spectroscopy ,Raman scattering - Abstract
Well-resolved vibrational spectra of LH2 complex isolated from two photosynthetic bacteria, Rhodobacter sphaeroides and Ectothiorhodospira sp., were obtained using surface-enhanced resonance Raman scattering (SERRS) exciting into the Qx and the Qy transitions of bacteriochlorophyll a. High-quality SERRS spectra in the Qy region were accessible because the strong fluorescence background was quenched near the roughened Ag surface. A comparison of the spectra obtained with 590 nm and 752 nm excitation in the mid- and low-frequency regions revealed spectral differences between the two LH2 complexes as well as between the LH2 complexes and isolated bacteriochlorophyll a. Because peripheral modes of pigments contribute mainly to the low-frequency spectral region, frequencies and intensities of many vibrational bands in this region are affected by interactions with the protein. The results demonstrate that the microenvironment surrounding the pigments within the two LH2 complexes is somewhat different, ...
- Published
- 2000
- Full Text
- View/download PDF
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