Melanie David

First-Principles Study of the Adsorption of Water on Tri-s-triazine-based Graphitic Carbon Nitride

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.

Adsorption of O2 on Cobalt-(n)Pyrrole Molecules from First-Principles Calculations

In order to clarify the adsorption mechanism of the O 2 molecule on Co–polypyrrole composite metallo-organic catalyst, we have investigated the interaction between the molecule and Co–( n )pyrrole model clusters ( n =4,6) using the density functional theory. The stable adsorption site of the O 2 molecule on Co–(4)pyrrole is found to be at the O–O center of mass located on top of the Co atom in side-on configuration, while for the case of Co–(6)pyrrole cluster, the O 2 molecule is slightly deviated from the side-on configuration. The O–O bonds of the O 2 /Co–(4)pyrrole and the O 2 /Co–(6)pyrrole systems have elongated by 10.84 and 9.86%, respectively. The elongation mechanism of O 2 on Co–( n )pyrrole is induced by the interaction between the cobalt d -orbitals and the O 2 anti-bonding π * orbital, which results in a charge transfer from the cobalt atom toward the O 2 molecule. This effect seems important in the adsorption of the O 2 molecule on Co–( n )pyrrole. It is likely that the extra charge in the O ...

Reactive Ion Etching Process of Transition-Metal Oxide for Resistance Random Access Memory Device

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.

CO adsorption effects on the electronic properties of Fe tape-porphyrin

We investigated the electronic properties of Fe tape-porphyrin and the effect of CO adsorption on it within the framework of density functional theory. As for the numerical results, we found that the Fe tape-porphyrin is metallic, and that the CO-adsorbed Fe tape-porphyrin is an insulator. Comparing the electronic structures of the Fe porphyrin molecule and the CO-adsorbed one, we found that the metal-insulator transition is caused by the hybridization of the d(xz) and d(yz) orbitals of Fe with the π(g)(*) orbital of CO.

Hydrogen peroxide adsorption on Fe-filled single-walled carbon nanotubes: a theoretical study

We investigated the adsorption of hydrogen peroxide molecules on Fe-filled single-walled carbon nanotubes (SWNTs) based on density functional theory (DFT) calculations. The adsorption possibilities for the hydrogen peroxide molecule were tested by finding the minimum energy as a function of distance of the molecule from the Fe-filled SWNT. Stable structures were obtained by optimizing the hydrogen peroxide (H(2)O(2)) as it was adsorbed on to the Fe-filled SWNT. This study may serve as an initial investigation into the possibility of Fe-filled single-walled carbon nanotubes (SWNTs) as catalyst material for the proton exchange membrane fuel cell (PEMFC).

Carbon nanoarch encapsulating Fe nanowire on Ni(111)

We investigate the stable structures of single-walled carbon nanotubes (SWNTs) on Ni(111) and when a SWNT is filled with Fe wire on Ni(111), based on density functional theory. We find stable geometries and electronic states for the nanotube on Ni(111). We propose the possibility that the C–C bonds of a carbon nanotube are broken by an Fe wire and a Ni surface. That is, when an Fe-filled SWNT (3,3) adsorbs on Ni(111) surface, the SWNT transforms into an arch-like structure.

Controllability of Electrical Conductivity by Oxygen Vacancies and Charge Carrier Trapping at Interface between CoO and Electrodes

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.

Polybutylene terephthalate on metals: a density functional theory and cluster models investigation

The strength of adhesion of polybutylene terephthalate (PBT) on aluminium is investigated using density functional theory-based energy calculations. The aluminium atom is connected to a PBT monomer at different orientations, and total energies are calculated and compared to determine the most stable orientation. The binding is strongest when the Al is oriented at 180° to the ester group of the monomer. Using this orientation as a basis, PBT adhesion on Ti, Ag, and Au is also investigated.

Adsorption of Fe and Co Nanowires to (3,3) Single-Walled Carbon Nanotubes

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.

Adsorption Properties of BF4- Anions on Graphene

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.