Reactive ion etching of transition-metal alloys

For production of advanced spin-electronic devices, such as a magnetic random access memory with the higher-density memory cell, a reactive ion etching (RIE) process of transition metal alloys is the indispensable component of development, while no transition-metal compounds with the relatively high vapor pressure have been founded so far. Here, we show the RIE process of a NiFe thin film by using CH4:O2:NH3 discharge. The RIE process was designed by ab initio calculations, and the present result is the first successful demonstration of the chemical effect in the RIE process for transition-metal alloys. The relative etching ratio of NiFe against Ti as the metal mask was decreased by substituting CH4 with CHF3

Catalytic reactivity of a transition metal (Pt, Pd, Ni and Cu) atom on cyclohexane dehydrogenation

We investigate and discuss the catalytic reactivity of a transition metal M (M: Pt, Pd, Ni and Cu) atom on cyclohexane dehydrogenation by performing total energy calculations, based on the density functional theory. Total atomic charge investigation along the reaction path shows that in breaking a C-H bond of the cyclohexane, the σ donation dominates for a Pd and Cu atom as compared with a Pt atom, and the π back-donation dominates for a Ni atom as compared with a Pt atom. Our results indicate that the excess charge transfer causes more energy required for breaking the C -H bond of the cyclohexane with a Pd, Ni and Cu atom

Hydrogen-induced lattice relaxation effects on the absorption and desorption of H on a Li(11) surface

Here, we investigate and discuss the effects of H-induced lattice relaxation on the H absorption into (desorption from) a Li(100) surface. Using the coupled-channel method via the local reflection matrix scheme, we performed quantum dynamics calculations to obtain the H absorption and desorption probability plots as functions of the H initial translational energy and the Li initial vibrational state. Our results show 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 (desorptin from) the surface (subsurface). At low initial translational energy of H, the Li lattice has sufficient time to relax effectively reducing the energy barrier for H absorption and desorption

Amino acid adsorption effects on nanotube electronics

We discuss effects of the adsorption of glycine, histidine, phenylalanine, and cysteine on the electronic structure of the metallic (3,3) carbon nanotube through calculations within density functional theory. Results show good nanotube electronic structure stability in the presence of the biomolecules. Molecule-nanotube band mixing and band degeneracy lifting are observed, though the limited extents to which these effects are manifested on the system electronics affirm the weak, noncovalent connection at their interface

Ab initio study of cyclohexane dehydrogenation on Pt(111)

We investigate cyclohexane dehydrogenation on Pt(111) by performing total energy calculations based on the density functional theory (DFT). After interacting with the Pt, the Pt draws an H atom from the cyclohexane, and an H-Pt bond is formed. With the C-H bond broken, cyclohexyl intermediate (C 6H11) desorbs from Pt(111). The cleaved H atom, then, moves to the hollow site of Pt(111), and the desorbing cyclohexyl comes back to and adsorbs on Pt(111). The C-H bond cleavage requires an activation barrier of 1.18 eV, which is a little lower than that with a small Pt cluster

Suppression of carrier spin polarization in diluted ferromagnetic semiconductors

We present a theoretical method for studying diluted magnetic semiconductors, extending the dynamical cluster approximation. The precursor effects of the localization and the direct exchange interaction between magnetic impurities can be considered in the method. We apply the method to the two-dimensional square lattice system with random localized spins. We show that the strong antiferromagnetic superexchange interaction between nearest-neighbor sites suppresses the polarization of the carrier spin

Density functional study on the interaction of hydrogen with Pt 3Ti(111)

We investigate the catalytic property of the intermetallic compound Pt 3Ti by studying the interaction of its (111) surface with hydrogen. Based on density functional theory, we obtain the 2-D PES to estimate the barrier for H2 dissociation, and the binding energy of H atom at different sites of the substrate. The observed energetics can be explained in terms of the role played by the Ti atoms in the compound. Our results show that the Ti atoms function as inactive components that dilute the concentration of the active Pt components thus making the compound less active than Pt towards hydrogen

Reactive ion etching of NiFe thin films from first-principles study: A case study

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/O 2(/NH3,H2) enable the NiFe surface to be etched. © 2005 The Japan Society of Applied Physics

Density functional theory investigation of one-dimensional organic-metallic multiple-decked sandwich model

We investigate electric and magnetic properties of a benzene-iron complex chain [Fe(C6H6)]∞. By performing first principles calculation based on the spin-polarized density functional theory, we find that this system shows semiconducting behavior having magnetic moment. We also show that this system is stable due to the Fe atom

Dissociation and sticking of H2 on Mg(0001), Ti(0001) and La(0001) surfaces

We performed quantum dynamics calculations using previously obtained potential energy surfaces (PESs) for the dissociative adsorption of hydrogen molecule incident on a Mg(0001), Ti(0001), and La(0001) surface. Based on the sticking probability plots we obtained as functions of the incidence H 2 beam energy, La is the best material for hydrogen storage, followed by Ti, and then by Mg. This is due to the absence of an activation barrier in the H2/La(0001) system. Both H2/Ti(0001) and H 2/Mg(0001) systems have activation barriers, but the H 2/Ti(0001) system has a very small activation barrier far from the curved region of the reaction path, while the H2/Mg(0001) system has a high activation barrier close to the curved region along the reaction path. Our results also indicate that the sticking probability has some dependence on the vibrational state of the impending H2 molecule for the Mg, Ti and La surfaces. The degree of dependence still varies in each metal. Vibrational effect is most observed with Mg, followed by Ti, and then by La. © 2004 The Physical Society of Japan