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We synthesized graphene oxide?sulfonated polyether ether ketone (GO?SPEEK) composite membrane and compare its proton conductivity with that of Nafion? 117 and SPEEK membranes. From experimental measurements, we found that GO?SPEEK has better proton conductivity (?GO?SPEEK = 3.8 × 10?2 S cm?1) when compared to Nafion? 117 (?Nafion = 2.4 × 10?2 S cm?1) and SPEEK (?SPEEK = 2.9 × 10?3 S cm?1). From density functional theory (DFT-) based total energy calculations, we found that GO?SPEEK has the shortest proton diffusion distance among the three membranes, yielding the highest tunneling probability. Hence, GO?SPEEK exhibits the highest conductivity. The short proton diffusion distance in GO?SPEEK, as compared to Nafion? 117 and SPEEK, can be attributed to the presence of oxygenated functional groups of GO in the polymer matrix. This also explains why GO?SPEEK requires the lowest hydration level to reach its maximum conductivity. Moreover, we have successfully shown that the proton conductivity ? is related to the tunneling probability T, i.e., ? = ?' exp(?1/T). We conclude that the proton diffusion distance and hydration level are the two most significant factors that determine the membrane's good conductivity. The distance between ionic sites of the membrane should be small to obtain good conductivity. With this short distance, lower hydration level is required. Thus, a membrane with short separation between the ionic sites can have enhanced conductivity, even at low hydration conditions.

We investigate the interaction of molecular hydrogen with the Pt surface. In particular, we calculate the potential energy surfaces (PESs) corresponding to the dissociative adsorption of H2 at different symmetric sites on the Pt(111) surface and for parallel and perpendicular orientations of H2 with respect to the surface, on the basis of the density functional theory. The PES results show the dependence of the activation barriers on the H2 adsorption site and orientation relative to the surface. For parallel orientations, the barrier is lowest (almost zero) when the H2 center of mass (CM) is directly above the top site while the H atoms are directed towards the hcp and fcc hollow sites. The activation barriers for the perpendicular orientation are always much higher than those for the parallel orientation, which indicates that the parallel orientation is favored for H2 adsorption. This result also suggests that an incident H2 initially in a nonparallel (e.g., perpendicular) orientation tends to reorient itself towards a parallel orientation where it is easier for H2 to be adsorbed.

We investigate the magnetic and electronic properties of Fe and Co nanowires adsorbed outside the wall of single-walled carbon nanotubes (SWNTs). We find that in Fe nanowire adsorption, the SWNT transforms into a diamond ring-like structure because of the charge transfer from the C–C bonds to the Fe–C bonds. In addition, the number of bands that crosses the Fermi level can be enhanced by adsorbing Fe and Co atoms.

We investigate the solvent effects of water, methanol and ethanol on the anionic (–SO3-) and acid (–SO3H) forms of the Nafion side chain using ab initio density functional calculations. The polarizable continuum model (PCM) and the explicit solvent molecule additive are used to represent the solvent. The alcohol molecule can more strongly interact with the proton of the acid form than a water molecule, indicating that the proton tends to trap the alcohol molecule.

The reactive ion etching (RIE) of the binary transition-metal oxides (TMOs) NiO, CuO and CoO, which are expected to be key materials of resistance random access memory (RRAMTM), was investigated. We found that inductively coupled plasma using CHF3-based discharge, which is highly compatible with conventional semiconductor RIE, is effective for the TMOs studied here. Furthermore, device fabrication using Pt/CoO/Pt trilayers is carried out, and a large change in resistance, which is an essential functionality of RRAM, was successfully observed. This should be definite evidence of a successful RIE realized in the present device fabrication.

We have investigated the electronic and magnetic properties of (3, 3) and (4, 4) single-walled carbon nanotubes (SWNTs) filled with 3d transition metal (TM) monatomic chains, using first-principles calculations based on the density functional theory to get a thorough understanding of metal atom-filled carbon nanotubes. We have found that the magnetic moment of 3d TM-filled SWNTs decreases when the TM atom changes from smaller atomic radius to larger atomic radius or, when the diameter of the SWNT decreases. Specifically, the magnetic moment increases as the bonding strength between a TM atom and carbon atoms decreases.

We report the effects of straining and CO precover on H2 interaction with Pt determined by ab initio density functional calculations. Compressive (tensile) strain prevents (promotes) H2 dissociation and subsequent H adsorption. On the other hand, a CO neighbor prevents only H2 dissociation. Therefore, the catalytic activities for H2 dissociative adsorption are the best for realizing tensile-strained Pt, and the worst for realizing compressive-strained and CO-precovered Pt. We suggest that straining and/or CO precover can be used as a catalytic tailor for H2 dissociative adsorption.

We investigate the chemical reaction between a Cr transition-metal atom and sodium diethyldithiocarbamate (NaDDC), a complexing agent used to detect and extract Cr in human blood samples. Using density-functional-theory-based calculations, we determine their stable structures of Cr(DDC)2ODDC and Cr(DDC)3 complexes and obtain their dissociation energies. We found dissociation energies of -10.66 and -3.24 eV for Cr(DDC)2ODDC and Cr(DDC)3 complexes, respectively. Hence, on the basis of dissociation energies, we have verified that the reaction of NaDDC with Cr produces Cr(DDC)2ODDC as a major product.

In response to the current need for an efficient, safe, and compact system for storing hydrogen in mobile applications, a scheme for maximizing and controlling hydrogen storage in graphite is proposed by modifying substrate reactivity through the exploitation of intrinsic vibrational modes in pristine and fully-hydrogenated graphite systems. Calculations within density functional theory suggest that infrared radiation of distinct frequencies can be used to independently induce graphite lattice restructuring and recrystallization for promoting hydrogen uptake and discharge, respectively. Effects of the initial attachment of hydrogen on graphite sheets are discussed, with computational results showing that additional hydrogen adsorption can proceed through easier reaction routes.

We investigate the effects of hydrogen-induced surface lattice relaxation on the dynamics of hydrogen absorption into the surface and desorption from the subsurface to the Pd(111) surface. We perform quantum dynamics calculations with and without surface lattice motion. From the results of both hydrogen absorption and desorption probability, we can see that the hydrogen motion and the surface lattice relaxation are dynamically coupled and, depending on the initial conditions, the surface lattice motion either promotes or hinders the penetration of hydrogen into (desorption from) the surface (subsurface). We observe tunneling of hydrogen through the energy barrier hindering the hydrogen from penetration into (desorption from) the surface (subsurface). We also investigate the surface temperature dependence of hydrogen absorption dynamics. From the results, we can see that the absorption probability increases (decreases) as the surface temperature increases in the low (high) hydrogen's initial translational energy regions.

We carry out first principles calculations to study the magnetic properties of a multilayer structure consisting of one monolayer (ML) of Co (Co1ML) on top of two ML of Ni (Ni2ML) deposited on top of Cu(111), i.e., Co1ML/Ni2ML/Cu(111). We found that the magnetic anisotropy of the Co1ML/Ni2ML multilayer does not change much with variation in the in-plane and inter-layer structures of the Co/Ni multilayer. On the other hand, interaction with the Cu(111) plays an important role. As a result of the electron transfer from the Cu(111) substrate to the first deposited Ni-layer, i.e., Ni(1), there is a reduction in the magnetic moment of Ni(1) and an increase in the magnetic crystalline anisotropy energy of Co1ML/Ni2ML/Cu(111) multilayer structure.

We present the results of density functional theory calculation in oxygen dissociative adsorption process on two types of isolated platinum (Pt) clusters: Pt4 and Pt10, by taking into account the effect of cluster reconstruction. The strength of Pt–Pt bonds in the clusters is mainly defined by d–d hybridization and interstitial bonding orbitals (IBO). Oxygen that adsorbed on the clusters is weakening the IBO and thus inducing geometry reconstruction as occurred in Pt10 cluster. However, cluster that could undergo structural deformation is found to promote oxygen dissociation with no energy barrier. The details show that maintaining well-balanced of attractive and repulsive (Hellmann–Feynman) forces between atoms is considered to be the main key to avoid any considerable rise of energy barrier. Furthermore, a modest energy barrier that gained in Pt4 cluster is presumed to be originate from inequality of intramolecular forces between atoms.

We have investigated the dissociative adsorption process of O2 (oxygen molecule) on a composite surface formed by coating a single platinum (Pt) adatom on a gamma-alumina (γ-Al2O3) (111) surface. This process is studied by using density functional theory (DFT) and described in terms of potential energy surfaces (PES) with respect to the molecular degrees of freedom. We compare the activation barriers and adsorption energies among typical reaction channels. Our results show that O2 dissociative adsorption is preferably occurred when this O2 molecule approaches the surface with molecular orientation inclined by 30° angle with respect to the surface normal, i.e., the condition with lowest activation barrier. The results indicate that dissociated O atoms are likely to form strong bonds with the Pt adatom by keeping distance from the alumina layer.

Recently, the role of resistance random access memory (RRAM) is becoming extremely important in the development of nonvolatile memories. RRAM works by changing the resistance of the transition metal oxide contained in RRAM after the application of a sufficiently high voltage, however, this switching mechanism has not been fully clarified. In this study, by performing first principles calculations based on the density functional theory, we first investigate the change in the property of bulk CoO resulting from oxygen vacancies and charge carrier trapping in the vicinity of the oxygen vacancies. Next, we perform calculations for slab models of CoO in contact with Ta, W, and Pt electrodes and hence investigate the effects of oxygen vacancies at the interface between the CoO layer and the electrode layer. On the basis of the obtained results, we conclude that W is the most suitable electrode material compared with Ta and Pt.

We have investigated the interaction between cobalt–(6)pyrrole [Co–(6)Ppy] clusters and O2 molecule, including the adsorption and dissociation of O2 molecule using the density functional theory (DFT) calculations. We found that O2 molecule is adsorbed on Co–(6)Ppy clusters with side-on configuration and the O–O bond length elongated around 10%. The elongation of the O–O bond when O2 is adsorbed on the clusters will weaken the O–O bond and increase the reactivity of the molecule. The calculated dissociation energies of O2 molecule on Co–(6)Ppy clusters span from 0.89 to 1.23 eV. The order of the dissociation energy is affected by the amount of the charge transferred from Co–(6)Ppy clusters to the O2 molecule in the transition state.

This study deals with the effect of the isomorphic substitution on the sorption of two Li atoms on montmorillonite using density functional theory (DFT). The isomorphic substitution is carried out by modifying the atomic composition of the upper tetrahedral layer of the montmorillonite by replacing one Si atom with one Al atom on the said position. Note that in the conventional structure, Si atom is located at the upper tetrahedral layer of montmorillonite. Results show that one Li atom is likely to be situated in the vacant tetrahedral site and the other one is in the vacant octahedral site, for both of the two montmorillonite systems (isomorphic substitution and conventional structure). The sorption energy was found to be -6.31 eV at the most stable configuration, that is for the isomorphic substitution.

The dissociation and adsorption processes of N2 on Pd(111) and Pd3Ag(111) surfaces are investigated using density functional theory (DFT). The dissociation of N2 molecule on Pd(111) is most efficient if its center-of-mass (CM) is fixed on top of Pd atom while allowing the N atoms to dissociate on the hollow sites [hcp hollow–top–fcc hollow (h–t–f) configuration] with an activation barrier of 5.94 eV. In Pd3Ag(111), N2 also prefers dissociating along the h–t–f configuration but the activation barrier is higher, 6.01 eV, and is attributed to the presence of Ag atom. The local density of states (LDOS) of the d-orbital of surface atoms shows that the presence of Ag had reduced the density of states in the region around the Fermi level which causes the higher activation barrier observed towards N2. Charge difference distribution also shows that there is a greater gain of charges of N2 from the surface atoms of Pd(111) surface which induces repulsion and resulting to the dissociation to individual N atoms. This further explains the easier dissociation and adsorption of N2 on Pd(111) as compared to Pd3Ag(111) surface.

In complex structures such as conjugated Si nanoparticles on carbon nanotubes (CNT), new properties arise out particle size control or nanoparticle–nanotube contact. In this work, the interaction of Si clusters (Si n , n=1–4) with metallic (5,5) single-wall carbon nanotube (SWCNT) is investigated using first principles calculations based on density functional theory, to show that electronic property of the Si/SWCNT system can change via Si–SWCNT conformation alone. Planar Si clusters on SWCNT exhibit the same metallic property regardless of size. However, once the planarity of Si n is lost, which happens when Si adsorption sites shifts towards the top and the Si–C bonds bend resulting to a buckled Si n configuration, a band gap of ∼0.32 eV in the entire Si/SWCNT system is introduced. The migration behavior of Si adatoms shows ease of cluster formation due to surface curvature. Such cluster formation can be accommodated by a distortion in the C–C bonds of CNT. Mechanism for the opening of the SWCNT band gap is presented.

As an initial step towards understanding the mechanism behind photocatalysis in graphitic carbon nitride (g-C3N4), we present a first-principles density functional theory (DFT) study of H2O molecular adsorption on the tri-s-triazine-based structure. The optimization of the system determined that the most stable configuration would be on top of the two-coordinated nitrogen atom in an orientation where one O–H bond is parallel to the surface and the other one is pointing to the surface. The adsorption energy at the most stable configuration was found to be 0.82 eV with a barrier energy of ∼0.02 eV. Partial density of states (PDOS) and charge density distribution analysis show that, primarily, the bonding occurs between the hydrogen atom of the water molecule and the two-coordinated nitrogen atom of g-C3N4. Results of this study would be useful not only to better understand the mechanism behind H2O molecule adsorption but also to give insight into the role of the catalyst in the photocatalytic process.

We investigated dissociative adsorption of H2 molecule on Pd3Ag(111) surface based on the constructed potential energy surfaces (PESs) from the results of first principles calculations. This study is performed to understand H2 dissociative adsorption mechanism on Pd3Ag(111) surface which acts as permeable film for H2 which is a product of biomass gasification. The PES results indicate that when the H2 molecule approaches the Ag atom of the 1st atomic layer, the activation barriers for dissociation start to increase. The dissociation of H2 on the surface has negligible activation barrier when the H2 center of mass (CM) is directly above the bridge site of Pd atoms while the hydrogen atoms are directed towards the hcp and fcc hollow sites. The average local density of states (LDOS) of the d-orbital of surface Pd atoms show peak in the region around the Fermi level which is not observed from the LDOS of the Ag atom in Pd3Ag(111) surface. This strongly supports the results of the constructed PES for H2 dissociative adsorption mechanism towards Pd3Ag(111) surface. This study will be significant for the design of hydrogen-permeable films which has applications on biomass-operated fuel cells.

We theoretically have been investigating the basic adsorption properties of BF4 - anions on graphene as the first step in researching the properties of carbon nanotube (CNT) electrodes in an electric double layer capacitor. To clarify the basic adsorption properties, we used the first principles calculation based on the density functional theory with the generalized gradient approximation for the exchange–correlation energy. As for the results, we found that the adsorbed configuration of BF4 - anions on graphene changes as their nearest neighbor distance decreases. We show that the electric dipole moment per unit area of BF4 - adsorbed on graphene increases as the nearest neighbor anion distance decreases. On the other hand, the electric dipole moment per BF4 - anion decreases as the nearest anion neighbor distance decreases. We also found that BF4 - anions adsorbed on both sides of graphene are more stable than those on one side.

ion reactions of copper from a (111) surface using halogen (F, Cl, and Br) atoms are studied as benchmark processes involving halogen-based etching agents. Reaction energetics are discussed, as well as potential energy surfaces that were created from ab initio energy calculations as functions of the center of mass and interatomic separation of the desorbing copper monohalide molecule. We support these results with a simple quantum dynamics model for the reaction leading to the desorption of CuF, which shows very high abstraction reaction probabilities. We also comment on analogous reactions on a Cu-terminated CuO surface.

We investigate the electric and magnetic properties of a benzene–vanadium complex chain [V(C6H6)]∞. By performing first principles calculation based on the spin-polarized density functional theory, we find that this system shows a half metallic ferromagnetic behavior, i.e., majority-spin (spin-up) electrons have a semiconducting band gap, while minority-spin (spin-down) electrons are metallic. We suggest that this ferromagnetic order is due to a double-exchange mechanism.

We performed quantum dynamics calculations using available potential energy surfaces for the dissociative adsorption of H2 incident on a Si(001)2×2 surface. In this study, we show that the probability of adsorption for H2 and the effect of vibrationally assisted sticking (VAS) vary at different sites along the Si-dimer bond. Based on the sticking probability plots for H2 as functions of its initial translational energy, we show that the H2-silicon surface interactions are all activated, with the lowest potential barrier being found in the case of H2 coming down the Si surface with its center of mass roughly above the down Si-dimer atom. On the other hand, the VAS effect is strongest when H2, while coming down the silicon surface along the surface normal, approaches the point farthest from the up Si-dimer atom along the Si-dimer bond. Here, the potential barrier is closest to the curved region along the reaction path in the corresponding potential energy surface for this system.

We investigate the electronic and magnetic properties of single-walled carbon nanotubes (SWNTs) filled with Fe nanowires, based on the spin-polarized density functional theory. We find that in the stable structure, the Fe-filled (3,3) and (5,0) SWNTs exhibit semiconducting properties, and the magnetic moment of Fe nanowires inside disappears. On the other hand, the Fe-filled (4,4), (5,5), (6,6) and (6,0) SWNTs, having larger radii, are metallic and exhibit ferromagnetic properties. The corresponding magnetic moment increases with increasing nanotube diameter.

We propose a reactive ion etching (RIE) process design from first-principles calculations for implementation to NiFe thin-film etching. We consider the interaction between the magnetic metal surface NiFe and various gases. We found that the gases CO/NH3, or CH3OH/O2(/NH3,H2) enable the NiFe surface to be etched.

In this present study, we investigate cyclohexane (C6H12) dehydrogenation process using a Pt cluster by performing total energy calculations based on density functional theory (DFT). We consider the process where cyclohexane initially approaches a Pt3 cluster. After interacting with the Pt cluster, the Pt cluster draws an H atom from the cyclohexane, and an H–Pt bond is formed. With a C–H bond broken, the cyclohexyl intermediate (C6H11) desorbs from the Pt cluster. Since the most stable structures of C6H10 and C6H9 are obtained by removing H atoms from the adjacent C atoms of the cyclohexane, we suggest that cyclohexane dehydrogenation process involves the sequential cleavage of one H atom at a time from the cyclohexane.

We consider singlet and triplet iron-porphyrin-O2 (FeP-O2) adducts to investigate spin polarization effects on the FeP-O2 interaction using ab initio calculations based on density functional theory (DFT). The presence of the imidazole (Im) ligand induces spin polarization from O2 to Fe in the triplet (Im)FeP-O2 adduct. The O-O bond of the triplet (Im)FeP-O2 is weaker than that of the triplet FeP-O2 because of this spin polarization effects. Our results suggest that magnetization of heme or heme-based nanomaterials may be utilized as cathode electrode catalysts in polymer electrolyte fuel cells (PEFCs).

We investigate the time-resolved two-photon photoemission (time-resolved 2PPE, TR2PPE) spectrum of the image state on Cu(111) by nonequilibrium perturbation theory. We show that, in the 2PPE process, the scattering of photoexcited quasiparticles (electrons and holes) due to Coulomb interactions between electrons causes excitation of secondary quasiparticles in the vicinity of the Fermi level as well as electron transitions to the image state. We demonstrate quantitatively on the basis of numerical results how the effect of relaxation of secondary quasiparticles is manifested in the TR2PPE spectrum.

Manifestations of the Kondo effect on an atomic length scale on and around a magnetic atom adsorbed on a nonmagnetic metal surface differ depending on which spectroscopic mode the scanning tunneling microscope is operated. In a series of reports, we showed that the Kondo effect can be directly observed as protrusions (peaks) in the spatial distribution of the tunneling current, and that the protrusions (peaks) observed in the spatial distribution of the tunneling current correspond to the resonances observed in the differential conductance spectra. In this report, we show that upon applying an external magnetic field with increasing magnitude, the protrusions (peaks) observed in the spin-resolved spatial distribution of the tunneling current would decrease monotonically for spin-down electrons, but change non-monotonically for spin-up electrons. We also show that, upon applying an external magnetic field, additional features about the Fermi level appear for the narrow dip structure observed for the corresponding differential conductance spectra.

The effects of three factors on the magnetoresistance in superlattices composed of magnetic and nonmagnetic slabs are studied within the framework of the coherent potential approximation: (i) the number of interfacial layers, in which magnetic and nonmagnetic ions are randomly distributed adjacent to interfaces between slabs, (ii) average distribution number and (iii) the relative position of electron energy levels of these ions. It is shown that the absolute value of the resistance is mainly determined by factors (i) and (ii), and that its magnetic-field-dependent part, on the other hand, is mainly determined by factor (iii).

The results of a model calculation are reported for magnetoresistance of artificial metallic multilayers. In the model, the main origin of the giant magnetoresistance in the multilayer is considered to be random distribution of magnetic and nonmagnetic ions at the interface. The effect of the random distribution of ions on the resistivity is estimated by the coherent potential approximation in each layer. The pattern behavior of the observed magnetoresistance seems to be reproduced qualitatively.