Showing papers by "Kwang S. Kim published in 2009"
TL;DR: The direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers is reported, and two different methods of patterning the films and transferring them to arbitrary substrates are presented, implying that the quality of graphene grown by chemical vapours is as high as mechanically cleaved graphene.
Abstract: Problems associated with large-scale pattern growth of graphene constitute one of the main obstacles to using this material in device applications. Recently, macroscopic-scale graphene films were prepared by two-dimensional assembly of graphene sheets chemically derived from graphite crystals and graphene oxides. However, the sheet resistance of these films was found to be much larger than theoretically expected values. Here we report the direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers, and present two different methods of patterning the films and transferring them to arbitrary substrates. The transferred graphene films show very low sheet resistance of approximately 280 Omega per square, with approximately 80 per cent optical transparency. At low temperatures, the monolayers transferred to silicon dioxide substrates show electron mobility greater than 3,700 cm(2) V(-1) s(-1) and exhibit the half-integer quantum Hall effect, implying that the quality of graphene grown by chemical vapour deposition is as high as mechanically cleaved graphene. Employing the outstanding mechanical properties of graphene, we also demonstrate the macroscopic use of these highly conducting and transparent electrodes in flexible, stretchable, foldable electronics.
10,033 citations
TL;DR: In this paper, a variation of the work function for single and bilayer graphene devices measured by scanning Kelvin probe microscopy (SKPM) is reported, by using the electric field effect, which can be adjusted as the gate voltage tunes the Fermi level across the charge neutrality point.
Abstract: We report variation of the work function for single and bilayer graphene devices measured by scanning Kelvin probe microscopy (SKPM). By use of the electric field effect, the work function of graphene can be adjusted as the gate voltage tunes the Fermi level across the charge neutrality point. Upon biasing the device, the surface potential map obtained by SKPM provides a reliable way to measure the contact resistance of individual electrodes contacting graphene.
1,205 citations
TL;DR: Variation of the work function for single and bilayer graphene devices measured by scanning Kelvin probe microscopy (SKPM) is reported, by use of the electric field effect.
Abstract: We report variation of the work function for single and bi-layer graphene devices measured by scanning Kelvin probe microscopy (SKPM). Using the electric field effect, the work function of graphene can be adjusted as the gate voltage tunes the Fermi level across the charge neutrality point. Upon biasing the device, the surface potential map obtained by SKPM provides a reliable way to measure the contact resistance of individual electrodes contacting graphene.
1,130 citations
TL;DR: A pincer-like benzene-bridged sensor with a pyrene excimer as a signal source and imidazolium as a phosphate anion receptor was synthesized and investigated for ATP sensing.
Abstract: A pincer-like benzene-bridged sensor 1 with a pyrene excimer as a signal source and imidazolium as a phosphate anion receptor was synthesized and investigated for ATP sensing. A unique switch of excimer vs monomer pyrene fluorescence of 1 is observed in the presence of ATP due to the charcteristic sandwich pi-pi stacking of pyrene-adenine-pyrene. On the other hand, four other bases of nucleoside triphosphates such as GTP, CTP, UTP, and TTP can interact only from the outside with the already stabilized stacked pyrene-pyrene dimer of 1, resulting in excimer fluorescence quenching. The fluorescent intensity ratio of monomer-to-excimer for 1 upon binding with ATP (I(375)/I(487)) is much larger than that upon binding with ADP and AMP. This difference is large enough to discriminate ATP from ADP and AMP. As one of the biological applications, sensor 1 is successfully applied to the ATP staining experiments. Sensor 1 is also applied to monitor the hydrolysis of ATP and ADP by apyrase. The results indicate that 1 is a useful fluorescent sensor for investigations of ATP-relevant biological processes.
540 citations
TL;DR: Lee et al. as mentioned in this paper used nanoscale spherical lenses that self-assemble by bottom-up integration of cup-shaped organic molecules called calixarenes to obtain near-field features of the order of 200 nm.
Abstract: The performance of a light microscope is intrinsically constrained by the Abbe diffraction limit. No matter how close to optical perfection it is, an imaging system cannot resolve two objects that are beyond this natural limit, which is dependent on the wavelength of the observed light and its angular distribution. Several methods have been devised to beat the diffraction limit, but these have generally required esoteric excitation schemes, so remain impractical. Lee et al. are working on a new way of beating the limit, using nanoscale spherical lenses that self-assemble by bottom-up integration of cup-shaped organic molecules called calixarenes. Lenses produced in this way have very short focal lengths that can generate near-field magnification beyond the diffraction limit, enabling the resolution of features of the order of 200 nm. The lenses can be placed at will on a surface and, among other things, can be used to reduce the size of deep-ultraviolet lithography features. Cup-shaped molecules of calix[4]hydroquinone self-assemble on a surface into a lens shape; these lenses are shown to generate near-field magnification beyond the diffraction limit, enabling the resolution of features of the order of 200 nanometres. Such spherical nanolenses provide new pathways for lens-based near-field focusing and high-resolution optical imaging at very low intensities, which are useful for, among other things, bio-imaging and near-field lithography. It is well known that a lens-based far-field optical microscope cannot resolve two objects beyond Abbe’s diffraction limit. Recently, it has been demonstrated that this limit can be overcome by lensing effects driven by surface-plasmon excitation1,2,3, and by fluorescence microscopy driven by molecular excitation4. However, the resolution obtained using geometrical lens-based optics without such excitation schemes remains limited by Abbe’s law even when using the immersion technique5, which enhances the resolution by increasing the refractive indices of immersion liquids. As for submicrometre-scale or nanoscale objects, standard geometrical optics fails for visible light because the interactions of such objects with light waves are described inevitably by near-field optics6. Here we report near-field high resolution by nanoscale spherical lenses that are self-assembled by bottom-up integration7 of organic molecules. These nanolenses, in contrast to geometrical optics lenses, exhibit curvilinear trajectories of light, resulting in remarkably short near-field focal lengths. This in turn results in near-field magnification that is able to resolve features beyond the diffraction limit. Such spherical nanolenses provide new pathways for lens-based near-field focusing and high-resolution optical imaging at very low intensities, which are useful for bio-imaging, near-field lithography, optical memory storage, light harvesting, spectral signal enhancing, and optical nano-sensing.
341 citations
TL;DR: The π(+)-π(D) complexes are found to be distinctly different from the π-π complexes and the non-π organic or metallic cation-π complex, while both complexes have similar percentage contributions from electrostatic and exchange energy components.
Abstract: We have investigated various types of π-interactions, where one of the interacting π-systems is represented by an aromatic benzene molecule. The system includes Rg-π, CH-π, π-π(D), π-π(T), H-π(T), π+-π(D), π+-π(T), H+-π(T), π+2-π(D), M+-π, and M+2-π complexes, where Rg denotes a rare gas or noble atom, M denotes a metal, and D/T indicates displaced-stacked/T-shaped structure. The microsolvation effect is also considered. We note that the interaction between a cationic π system and a neutral π system (πcation-π interaction) is so far ambiguously considered as either π-π or cation-π interaction. In terms of total binding energy, the πcation-π interaction is weaker than the cation−π interaction, but much stronger than the π-π interaction. When the hydrophilic (N−H)+ or (C−H)+ group in a singly charged π+ system (as in protonated histidine, arginine, pyridine, or dimethyl imidazolium) interacts with a π-system, the complex favors a T-shaped form [π+-π(T) complex]. However, in the presence of polar solvating m...
245 citations
TL;DR: This critical review provides an extensive survey of on-going research and its current status in molecular electronics with the focus on theoretical applications to diverse types of devices along with a brief introduction of theoretical methods and its practical implementation scheme.
Abstract: Rapid progress of nanotechnology requires developing novel theoretical methods to explain complicated experimental results and predict new functions of nanodevices. Thus, for the last decade, one of the challenging works of quantum chemistry is to understand the electron and spin transport phenomena in molecular devices. This critical review provides an extensive survey of on-going research and its current status in molecular electronics with the focus on theoretical applications to diverse types of devices along with a brief introduction of theoretical methods and its practical implementation scheme. The topics cover diverse molecular devices such as molecular wires, rectifiers, field effect transistors, electrical and optical switching devices, nanosensors, spin-valve devices, negative differential resistance devices and inelastic electron tunnelling spectroscopy. The limitations of the presented method and the possible approaches to overcome the limitations are addressed (183 references).
134 citations
TL;DR: Light is shed on the mechanisms involved in the loss of one molar equivalent of H(2) from solid lithium amidoboranes by using high-level ab initio calculations of monomeric and dimeric compounds in the gas phase for the design of future hydrogen-storage media.
Abstract: Hydrogen storage: In lithium amidoboranes an initial molecule of H2 is released by the formation of LiH, followed by a redox reaction of the dihydrogen bond formed between LiHδ− and NHδ+. In this dehydrogenation process, an intermolecular NB bond forms through the catalytic effect of a Li cation. After releasing the first molecule of H2, a Li cation binds to a nitrogen atom, lowering the energy barrier for the second H2 loss per lithium amidoborane dimer (see figure).
Alkali-metal amidoboranes have been recently highlighted as materials that satisfy many of the criteria required to make hydrogen-storage media. It is, therefore, crucial for us to understand the dehydrogenation mechanism of these materials for further development towards making successful hydrogen-storage media. In the present study, we attempt to shed light on the mechanisms involved in the loss of one molar equivalent of H2 from solid lithium amidoboranes by using high-level ab initio calculations of monomeric and dimeric compounds in the gas phase. In the lithium amidoborane dimer, H2 is released by the formation of LiH, which is followed by a redox reaction of the dihydrogen bond formed between the strongly basic H− in LiH and Hδ+ bonded to N. In the dehydrogenation process, the Li cation catalyzes the intermolecular NB bond formation; this could lead to new pathways for NB polymerization. After the release of the first molecule of H2, a Li cation binds to a nitrogen atom, resulting in a lowering of the energy barrier for the second dehydrogenation process per dimer. These results will be useful for the design of future hydrogen-storage media.
103 citations
TL;DR: It is demonstrated that the adsorbed fullerol activates TiO(2) under visible-light irradiation through the "surface-complex CT" mechanism, which is largely absent in the C(60)/TiO (2) system.
Abstract: The development of visible-light-active photocatalysts is being investigated through various approaches. In this study, C(60)-based sensitized photocatalysis that works through the charge transfer (CT) mechanism is proposed and tested as a new approach. By employing the water-soluble fullerol (C(60)(OH)(x)) instead of C(60), we demonstrate that the adsorbed fullerol activates TiO(2) under visible-light irradiation through the "surface-complex CT" mechanism, which is largely absent in the C(60)/TiO(2) system. Although fullerene and its derivatives have often been utilized in TiO(2)-based photochemical conversion systems as an electron transfer relay, their successful photocatalytic application as a visible-light sensitizer of TiO(2) is not well established. Fullerol/TiO(2) exhibits marked visible photocatalytic activity not only for the redox conversion of 4-chlorophenol, I(-), and Cr(VI), but also for H(2) production. The photoelectrode of fullerol/TiO(2) also generates an enhanced anodic photocurrent under visible light as compared with the electrodes of bare TiO(2) and C(60)/TiO(2), which confirms that the visible-light-induced electron transfer from fullerol to TiO(2) is particularly enhanced. The surface complexation of fullerol/TiO(2) induced a visible absorption band around 400-500 nm, which was extinguished when the adsorption of fullerol was inhibited by fluorination of the surface of TiO(2). The transient absorption spectroscopic measurement gave an absorption spectrum ascribed to fullerol radical cations (fullerol(*+)) the generation of which should be accompanied by the proposed CT. The theoretical calculation regarding the absorption spectra for the (TiO(2) cluster+fullerol) model also confirmed the proposed CT, which involves excitation from HOMO (fullerol) to LUMO (TiO(2) cluster) as the origin of the visible-light absorption.
100 citations
TL;DR: This work theoretically investigates the structures and binding characteristics of transition metal (TM) cations including novel metal cations interacting with benzene (Bz), and exhibits intriguing binding characteristics, different from the typical cation-π interactions between alkaliMetal cations and aromatic rings.
Abstract: The cation-π interactions have been intensively studied. Nevertheless, the interactions of π systems with heavy transition metals and their accurate conformations are not well understood. Here, we theoretically investigate the structures and binding characteristics of transition metal (TM) cations including novel metal cations (TM(n+) = Cu(+), Ag(+), Au(+), Pd(2+), Pt(2+), and Hg(2+)) interacting with benzene (Bz). For comparison, the alkali metal complex of Na(+)-Bz is also included. We employ density functional theory (DFT) and high levels of ab initio theory including Moller-Plesset second-order perturbation (MP2) theory, quadratic CI method with single and double substitutions (QCISD), and the coupled cluster theory with single, double, and perturbative triple excitations (CCSD(T)). Each of the transition metal complexes of benzene exhibits intriguing binding characteristics, different from the typical cation-π interactions between alkali metal cations and aromatic rings. The complexes of Na(+), Cu(+), and Ag(+) favor the conformation of C6v symmetry with the cation above the benzene centroid (πcen). The formation of these complexes is attributed to the electrostatic interaction, while the magnitude of charge transfer has little correlation with the total interaction energy. Because of the TM(n+)←π donation, cations Au(+), Pd(2+), Pt(2+), and Hg(2+) prefer the off-center π conformation (πoff) or the π coordination to a C atom of the benzene. Although the electrostatic interaction is still important, the TM←π donation effect is responsible for the binding site. The TM(n+)-Bz complexes give some characteristic IR peaks. The complexes of Na(+), Cu(+), and Ag(+) give two IR active modes between 800 and 1000 cm(-1),which are inactive in the pure benzene. The complexes of Au(+), Pd(2+), Pt(2+), and Hg(2+) give characteristic peaks for the ring distortion, C-C stretching, and C-H stretching modes as well as significant red-shifts in the CH out-of-plane bending.
69 citations
TL;DR: One-dimensional single-crystalline rectangular nanotubes (RNTs) of 5,10,15,20-tetra(4-pyridyl)porphyrin (H(2)TPyP) are synthesized by a vaporization-condensation-recrystallization process and form by self-stacking of H(2), through hydrogen-bonding, H-pi, and pi-pi intermolecular interactions.
Abstract: Stacking up: One-dimensional single-crystalline rectangular nanotubes (RNTs) of 5,10,15,20-tetra(4-pyridyl)porphyrin (H(2)TPyP, see picture) are synthesized by a vaporization-condensation-recrystallization process. The single-crystal X-ray diffraction and selected-area electron diffraction data reveal that the H(2)TPyP RNTs form by self-stacking of H(2)TPyP units through hydrogen-bonding, H-pi, and pi-pi intermolecular interactions.
TL;DR: Two previously reported structures of the water dimer cation [disproportionated ionic (Ion) structure and hydrazine-like (OO) structure] are compared and it is indicated that the ionization of water clusters produce the hydronium cation moiety (H3O(+)) and the hydroxy radical.
Abstract: By using density functional theory (DFT) and high-level ab initio theory, the structure, interaction energy, electronic property, and IR spectra of the water dimer cation [(H2O)2(+)] are investigated. Two previously reported structures of the water dimer cation [disproportionated ionic (Ion) structure and hydrazine-like (OO) structure] are compared. For the complete basis set (CBS) limit of coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)], the Ion structure is much more stable (by 11.7 kcal/mol). This indicates that the ionization of water clusters produce the hydronium cation moiety (H3O(+)) and the hydroxy radical. The transition barrier for the interconversion from the Ion/OO structure is ∼15/∼9 kcal/mol. It is interesting to note that the calculation results of the water dimer cation vary seriously depending on calculation methods. Moller-Pleset second-order perturbation (MP2) theory gives reasonable relative energies in favor of the Ion structure but reports unreasonable frequencies for the OO structure. On the other hand, most DFT calculations with various functionals overstabilize the OO structure. However, the DFT results with MPW1K and BH&HLYP functionals are very close to the CCSD(T)/CBS results. Thus, as for the validity test of the DFT functionals for ionized molecular systems, the energy comparison of two water dimer cation structures would be a very important criterion.
TL;DR: It is shown that the band structure and surface density of states of an electrode material, independent of the choice of other device components, have unique influences on the transmission curve.
Abstract: Understanding the effects of each component of a molecular device is at the heart of designing a useful device. Molecular cores and linkers are well studied, but relatively few studies have been devoted to investigating the electrode effect on a molecular electronic device. Here, we study unique characteristics of Au, Ru, and carbon nanotube electrodes using the nonequilibrium Green function method combined with a density functional theory. By systematic modification of the device region, we extract the effect of the electrode materials on the electron transport. We show that the band structure and surface density of states of an electrode material, independent of the choice of other device components, have unique influences on the transmission curve. We note that carbon nanotube electrodes can offer unusual nonlinear current-voltage characteristics.
TL;DR: This work investigated the issue of two-dimensional versus three-dimensional structures for neutral-state Au10 and clarified the lowest-energy structure among a few 2D Au10(-) isomers and carried out high levels of ab initio calculations of Möller-Plesset second order perturbation theory (MP2), and coupled cluster theory with single and double excitations (CCSD) including perturbative triple excitations [CCSD(T].
Abstract: We have investigated the issue of two-dimensional (2D) versus three-dimensional (3D) structures for neutral-state Au10 and clarified the lowest-energy structure among a few 2D Au10(-) isomers. Though almost all previous works were based on density functional theory (DFT), we here carried out not only extensive DFT calculations but also high levels of ab initio calculations of Moller-Plesset second order perturbation theory (MP2), and coupled cluster theory with single and double excitations (CCSD) including perturbative triple excitations [CCSD(T)]. While DFT favors 2D structures, MP2 and CCSD(T) favor 3D structures for moderate-sized basis sets. However, we note that the basis-set superposition error (BSSE) corrections make the ab intio results favor 2D structures too. The near-degeneracy (driven by relativistic effects) of 5d and 6s orbitals of gold helps stabilize acute apex gold atoms, resulting in 2D structures. The planar triangular structures of a local minimum Au10 (triplet) and the global minimum Au10(-) show remarkable spatial charge-spin separation due to their singly occupied molecular orbital(s). By the same reason, Au10(-) shows much larger vertical detachment energy than other even-numbered gold cluster anions.
TL;DR: A highly selective receptor for serotonin was designed using cages formed by the (R)-lipo-diaza-18-crown-6 self-assembled monolayer on gold and experimentally verified by a variety of electrochemical experiments in solutions containing large amounts of dopamine and ascorbic acid.
Abstract: A highly selective receptor for serotonin was designed using cages formed by the (R)-lipo-diaza-18-crown-6 self-assembled monolayer (SAM) on gold and experimentally verified by a variety of electrochemical experiments in solutions containing large amounts of dopamine and ascorbic acid, as well as other interferents. The molecular modeling study showed that parameters such as the H-pi interaction provided important driving forces for the cage to form a strong inclusion complex with serotonin. The charge-transfer resistance (R(CT)'s) to/from redox probe ions, Fe(CN)(6)(3-/4-), was greatly enhanced because of their electrostatic attractions to ammonium ions of serotonin molecules captured by cages. The changes in R(CT)-values were shown to be remarkably selective for serotonin in the presence of many interferents.
TL;DR: Geometries obtained at the DFT/MO6-2X and MP2/aug-cc-pVDZ levels, combined with highly accurate energy calculations at the complete basis set (CBS) limit of CCSD(T), establish formation of the displaced pi-stacked heterodimer between phenylacetylene and 1,3,5-triazine.
Abstract: The IR-UV double resonance spectroscopy of a complex between phenylacetylene and 1,3,5-triazine reveals that the acetylene C–H group of phenylacetylene is minimally perturbed due to its interaction with 1,3,5-triazine. Further, the IR spectrum clearly indicates that 1,3,5-triazine primarily interacts with π-electron density of the benzene ring in phenylacetylene. Geometries obtained at the DFT/MO6-2X and MP2/aug-cc-pVDZ levels, combined with highly accurate energy calculations at the complete basis set (CBS) limit of CCSD(T), establish formation of the displaced π-stacked heterodimer between phenylacetylene and 1,3,5-triazine.
Patent•
27 Mar 2009TL;DR: In this paper, a secondary chamber within a reactor chamber is placed to restrict a flow to provide a laminar flow, and inner shells can be successively extracted from multi-walled carbon nanotubes (MWNTs) by applying a lateral force to an elongated tubular sidewall at a location between its two ends.
Abstract: Ultralong carbon nanotubes can be formed by placing a secondary chamber within a reactor chamber to restrict a flow to provide a laminar flow. Inner shells can be successively extracted from multi-walled carbon nanotubes (MWNTs) such as by applying a lateral force to an elongated tubular sidewall at a location between its two ends. The extracted shells can have varying electrical and mechanical properties that can be used to create useful materials, electrical devices, and mechanical devices.
TL;DR: In this article, scaling expressions for the free energy are derived, using the Luttinger-Ward functional approach in the Eliashberg framework, for two different models of quantum critical point (QCP).
Abstract: Scaling expressions for the free energy are derived, using the Luttinger-Ward (LW) functional approach in the Eliashberg framework, for two different models of quantum critical point (QCP). First, we consider the spin-density-wave (SDW) model for which the effective theory is the Hertz-Moriya-Millis (HMM) theory, describing the interaction between itinerant electrons and collective spin fluctuations. The dynamic of the latter are described by a dynamical exponent $z$ depending on the nature of the transition. Second, we consider the Kondo breakdown model for QCP's, one possible scenario for heavy-fermion quantum transitions, for which the effective theory is given by a gauge theory in terms of conduction electrons, spinons for localized spins, holons for hybridization fluctuations, and gauge bosons for collective spin excitations. For both models, we construct the thermodynamic potential, in the whole phase diagram, including all kinds of self-energy corrections in a self-consistent way, at the one loop level. We show how Eliashberg framework emerges at this level and use the resulting Eliashberg equations to simplify the LW expression for free energy . it is found that collective boson excitations play a central role. The scaling expression for the singular part of the free energy near the Kondo breakdown QCP is characterized by two length scales : one is the correlation length for hybridization fluctuations, and the other is that for gauge fluctuations, analogous to the penetration depth in superconductors.
TL;DR: Three isomers of 3D cage structure are much more stable in zero point energy corrected binding energy and in free binding energies at 150 K than the lowest energy netlike structures, while the netlike structure would be more stable around approximately 250 K.
Abstract: Protonated water clusters H+(H2O)n favor two-dimensional (2D) structures for n ≤ 7 at low temperatures. At 0 K, the 2D and three-dimensional (3D) structures for n = 8 are almost isoenergetic, and the 3D structures for n > 9 tend to be more stable. However, for n = 9, the netlike structures are likely to be more stable above 150 K. In this regard, we investigate the case of n = 10 to find which structure is more stable between the 3D structure and the netlike structure around 150 and 250 K. We use density functional theory, Moller−Plesset second-order perturbation theory, and coupled cluster theory with single, double, and perturbative triple excitations (CCSD(T)). At the complete basis set limit for the CCSD(T) level of theory, three isomers of 3D cage structure are much more stable in zero point energy corrected binding energy and in free binding energies at 150 K than the lowest energy netlike structures, while the netlike structure would be more stable around ∼250 K. The predicted vibrational spectra a...
TL;DR: In this paper, a 2D net-like structure with two acceptor (A) type dangling water molecules is shown to be the most stable in zero-point energy (ZPE) corrected binding energy at 0 K.
Abstract: It is not clearly known whether H+(H2O)9 has a 2-dimensional (2D) net-like structure or 3-dimensional (3D) structure. Thus, calculations have been carried out based on density functional theory [DFT], Moller–Plesset second- order perturbation theory (MP2), resolution of identity MP2 theory (RIMP2), and coupled cluster theory with single, double and perturbative triple excitations (CCSD(T)). For the complete basis set (CBS) limit at the CCSD(T) level of theory, two nearly isoenergetic 3D closed structures are the most stable in zero-point energy (ZPE) corrected binding energy at 0 K. However, at 150 K, there are three competing 2D net-like structures. The structure with two acceptor (A) type dangling water molecules is the most stable. This structure is in good agreement with the experimental symmetric and asymmetric OH stretching peaks for the free acceptor (A) type of dangling water molecule(s) at 3650 and 3742 cm−1. On the other hand, another structure shows a better spectral intensity pattern. Thus, th...
TL;DR: Using the difference in surface tension between SiO2 and metal catalysts (Mn2+, Ni2+), it is shown how metals form nanoshells, nanodiscs and nanospheres at the tips of theSiO2 nanostructures of nanocones, nanorods and nanowires.
Abstract: Utilizing the difference in surface tension between SiO2 and metal catalysts (Mn2+, Ni2+), we show how metals form nanoshells, nanodiscs and nanospheres at the tips of the SiO2 nanostructures of nanocones, nanorods and nanowires. For the Mn2+ catalyst (i), SiO2-nanocones are formed with the hemispherical convex cap of the MnO/SiO2 composite. For the Ni2+ catalyst (ii), SiO2 nanowires are grown due to the concave shape of SiO2 surrounding the multi-faceted NiSi particles at their tip. For the Mn2+/Ni2+ catalyst (iii), SiO2 nanorods are formed with large-sized spherical ferromagnetic single Ni nanocrystals (50-200 nm in diameter) surrounded by the concave MnO2/SiO2 composite at the tip of the SiO2 nanorods. This large-sized spherical formation of the single Ni crystal is possible because Ni is able to be chemically reduced by Mn at 950 degrees C, well below the melting point of Ni (1455 degrees C) due to the alloying effect.
TL;DR: In this article, the structure of hydrated hydride anion clusters was investigated using density functional theory and high-level ab initio theory, and new low-lying energy structures for H(H2O)n3,4,6 which are compatible with previously reported structures were found.
Abstract: We have reinvestigated the structures of hydrated hydride anion clusters, using density functional theory and high-level ab initio theory We find new low-lying energy structures for H(H2O)n3,4,6 which are compatible with previously reported structures The binding energies, electronic properties, and IR spectra of these competing low-energy hydrated hydride anion clusters are reported to facilitate experiments © 2009 Wiley Periodicals, Inc Int J Quantum Chem 109: 1820 -1826, 2009
TL;DR: A new ground state is proposed where the two single dangling bonds created by H(2) dissociation are antiferromagnetically coupled with each other, and such a spin ordering is found to be energetically favored over the previously proposed charge ordering.
Abstract: The dissociative adsorption of an H2 molecule on the Si(001) surface, which has been experimentally identified in terms of dissociation on one side of two adjacent Si dimers, is investigated by spin polarized density-functional calculations within the generalized-gradient approximation. In contrast to the prevailing nonmagnetic configuration of charge ordering, we propose a new ground state where the two single dangling bonds (DBs) created by H2 dissociation are antiferromagnetically coupled with each other. Such a spin ordering is found to be energetically favored over the previously proposed charge ordering. In the latter configuration, the buckling of the two DBs amounts to a height difference (Δh) of 0.63 A, caused by a Jahn–Teller-like distortion, while in the former configuration, their buckling is almost suppressed to be Δh=0.03 A as a consequence of spin polarization.
Journal Article•
TL;DR: In this article, independent and cumulative production cross-sections for the Ti-nat(p,x)V-48, Sc-43,Sc-44m, SC-449,SC-46,Sc 47,Sc 48,Sc 43,Sc 44m,Sc 46,Sc 49,Sc 50,Sc 51,Sc 52,Sc 53,Sc 54,Sc 56,Sc 57,Sc 58,Sc 59,Sc 60,Sc 61,Sc 62,Sc 63,Sc 64,Sc 69,Sc 70,Sc 72,Sc 73,
TL;DR: In this paper, a critical review provides an extensive survey of on-going research and its current status in molecular electronics with the focus on theoretical applications to diverse types of devices along with a brief introduction of theoretical methods and its practical implementation scheme.
Abstract: Rapid progress of nanotechnology requires developing novel theoretical methods to explain complicated experimental results and predict new functions of nanodevices. Thus, for the last decade, one of the challenging works of quantum chemistry is to understand the electron and spin transport phenomena in molecular devices. This critical review provides an extensive survey of on-going research and its current status in molecular electronics with the focus on theoretical applications to diverse types of devices along with a brief introduction of theoretical methods and its practical implementation scheme. The topics cover diverse molecular devices such as molecular wires, rectifiers, field effect transistors, electrical and optical switching devices, nanosensors, spin-valve devices, negative differential resistance devices and inelastic electron tunnelling spectroscopy. The limitations of the presented method and the possible approaches to overcome the limitations are addressed (183 references).