Transport Properties of Nanoscale Materials for Molecular Wire Applications: A Case Study of Ferrocene Dimers

Hiroshi Mizuseki,Rodion V. Belosludov,Tomoki Uehara,Sang Uck Lee,Yoshiyuki Kawazoe 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.4

Recently, molecular electronics has been attracting significant attention as a post-silicon enabling technology for the fabrication of future nanoscale electronic devices. The geometric and the electronic structures of the proposed configurations of ferrocene-based dimer systems, such as bisferrocene-2,4-dithiolate, s-(bisferrocenyl)indacene-2,6-dithiolate and bis(ferrocenyl)pentalene-2,5-dithiolate, were examined using density functional theory. The transport properties were investigated using the nonequilibrium Green's function formalism for quantum transport. The results obtained indicate that the transmission coefficients of the dimers strongly depend on the metal-metal distance and on delocalization of the molecular levels. Thus, control of molecular orbital delocalization can be achieved by designing the metallocene-based polymer such that the metal-metal distance is optimal. Recently, molecular electronics has been attracting significant attention as a post-silicon enabling technology for the fabrication of future nanoscale electronic devices. The geometric and the electronic structures of the proposed configurations of ferrocene-based dimer systems, such as bisferrocene-2,4-dithiolate, s-(bisferrocenyl)indacene-2,6-dithiolate and bis(ferrocenyl)pentalene-2,5-dithiolate, were examined using density functional theory. The transport properties were investigated using the nonequilibrium Green's function formalism for quantum transport. The results obtained indicate that the transmission coefficients of the dimers strongly depend on the metal-metal distance and on delocalization of the molecular levels. Thus, control of molecular orbital delocalization can be achieved by designing the metallocene-based polymer such that the metal-metal distance is optimal.

Tetrahexcarbon: A two-dimensional allotrope of carbon

Ram, Babu,Mizuseki, Hiroshi Elsevier 2018 Carbon Vol.137 No.-

<P><B>Abstract</B></P> <P>A two-dimensional structurally stable carbon allotrope is predicted using first-principles calculations. This unique network is composed of tetra and hexa-rings of carbon atoms known as Tetrahexcarbon. Tetrahexcarbon has a quasiparticle (QP) direct band gap of 3.70 eV at Γ , which is closer to the ZnS, a well-known direct bandgap semiconductor. Interestingly, it is dynamically stable and can withstand temperature up to 1000 K, which is confirmed by performing phonon and <I>ab initio</I> molecular dynamics (AIMD) simulations. The mobilities of both electrons and holes in this material are found to be anisotropic. It exhibits extraordinary room temperature in-plane electron mobility of order ∼ <SUP> 10 4 </SUP> <SUP> cm 2 </SUP> <SUP> V − 1 </SUP> <SUP> s − 1 </SUP> , which is an order of magnitude higher than the black phosphorus monolayer ( ∼ <SUP> 10 3 </SUP> <SUP> cm 2 </SUP> <SUP> V − 1 </SUP> <SUP> s − 1 </SUP> ) and two orders of magnitude higher than MoS<SUB>2</SUB> ( ∼ 200 <SUP> cm 2 </SUP> <SUP> V − 1 </SUP> <SUP> s − 1 </SUP> ) monolayer. The optical response of Tetrahexcarbon obtained by applying Bethe-Salpeter equation (BSE) to include excitonic effects on top of the partially self-consistent GW<SUB>0</SUB> calculation. The absorption onsets strongly depend on the light polarization directions indicating Tetrahexcarbon an anisotropic material.</P>

Mechanistic Insight into the Chemical Exfoliation and Functionalization of Ti₃C₂ MXene

Srivastava, Pooja,Mishra, Avanish,Mizuseki, Hiroshi,Lee, Kwang-Ryeol,Singh, Abhishek K. American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.36

<P>MXene, a two-dimensional layer of transition metal carbides/nitrides, showed great promise for energy storage, sensing, and electronic applications. MXene are chemically exfoliated from the bulk MAX phase; however, mechanistic understanding of exfoliation and subsequent functionalization of these technologically important materials is still lacking. Here, using density-functional theory we show that exfoliation of Ti3C2 MXene proceeds via HF insertion through edges of Ti3AlC2 MAX phase. Spontaneous dissociation of HF and subsequent termination of edge Ti atoms by H/F weakens Al-MXene bonds. Consequent opening of the interlayer gap allows further insertion of HF that leads to the formation of AlF3 and H-2, which eventually come out of the MAX, leaving fluorinated MXene behind. Density of state and electron localization function shows robust binding between F/OH and Ti, which makes it very difficult to obtain controlled functionalized or pristine MXene. Analysis of the calculated Gibbs free energy (Delta G) shows fully fluorinated MXene to be lowest in energy, whereas the formation of pristine MXene is thermodynamically least favorable. In the presence of water, mixed functionalized Ti3C2Fx(OH)(1-x) (x ranges from 0 to 1) MXene can be obtained. The Delta G values for the mixed functionalized MXenes are very close in energy, indicating the random and nonuniform functionalization of MXene. The microscopic understanding gained here unveils the challenges in exfoliation and controlling the functionalization of MXene, which is essential for its practical application.</P>

Temperature Dependence of the Bulk Modulus in fcc Metals by Using a Lattice-Gas Model with Renormalized Potentials

Ryoji Sahara,Hiroshi Mizuseki,Kaoru Ohno,Yoshiyuki Kawazoe 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.4

Temperature dependence of the bulk modulus in five fcc metals are analyzed by using a fcc lattice-gas model. To treat actual systems as quantitatively as possible, we introduce two empirical potentials, which have been widely used for molecular dynamics (MD) simulations. The potentials are mapped onto the fcc lattice by using the potential renormalization technique, which gives a reasonable way to map interatomic potentials, such as MD potentials, onto lattice models, in order to overcome the shortcomings of lattice-gas models of neglecting the internal entropy of the system. By comparing the results with experimental, MD and first-principles data, the renormalized potential is found to reproduce the temperature dependence of the bulk modulus well. Temperature dependence of the bulk modulus in five fcc metals are analyzed by using a fcc lattice-gas model. To treat actual systems as quantitatively as possible, we introduce two empirical potentials, which have been widely used for molecular dynamics (MD) simulations. The potentials are mapped onto the fcc lattice by using the potential renormalization technique, which gives a reasonable way to map interatomic potentials, such as MD potentials, onto lattice models, in order to overcome the shortcomings of lattice-gas models of neglecting the internal entropy of the system. By comparing the results with experimental, MD and first-principles data, the renormalized potential is found to reproduce the temperature dependence of the bulk modulus well.

Isolation of pristine MXene from Nb₄AlC₃ MAX phase: a first-principles study

Mishra, Avanish,Srivastava, Pooja,Mizuseki, Hiroshi,Lee, Kwang-Ryeol,Singh, Abhishek K. The Royal Society of Chemistry 2016 Physical Chemistry Chemical Physics Vol.18 No.16

<P>Synthesis of pristine MXene sheets from MAX phase is one of the foremost challenges in getting a complete understanding of the properties of this new technologically important 2D-material. Efforts to exfoliate Nb4AlC3 MAX phase always lead to Nb4C3 MXene sheets, which are functionalized and have several Al atoms attached. Using the first-principles calculations, we perform an intensive study on the chemical transformation of MAX phase into MXene sheets by inserting HF, alkali atoms and LiF in Nb4AlC3 MAX phase. Calculated bond-dissociation energy (BDE) shows that the presence of HF in MAX phase always results in functionalized MXene, as the binding of H with MXene is quite strong while that with F is weak. Insertion of alkali atoms does not facilitate pristine MXene isolation due to the presence of chemical bonds of almost equal strength. In contrast, weak Li-MXene and strong Li-F bonding in Nb4AlC3 with LiF ensured strong anisotropy in BDE, which will result in the dissociation of the Li-MXene bond. Ab initio molecular dynamics calculations capture these features and show that at 500-650 K, the Li-MXene bond indeed breaks leaving a pristine MXene sheet behind. The approach and insights developed here for chemical exfoliation of layered materials bonded by chemical bonds instead of van der Waals can promote their experimental realization.</P>

HYDROGEN STORAGE ON NANOFULLERENE CAGES

NATARAJAN SATHIYAMOORTHY VENKATARAMANAN,HIROSHI MIZUSEKI,YOSHIYUKI KAWAZOE 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2009 NANO Vol.4 No.5

In this paper, we discuss and compare various nanocage materials proposed theoretically as storage medium for hydrogen. Doping of transition elements leads to clustering which reduces the gravimetric density of hydrogen, while doping of alkali and alkali-earth metals on the nanocage materials, such as carborides, boronitride, and boron cages, were stabilized by the charger transfer from the dopant to the nanocage. Further, the alkali or alkali-earth elements exist with a charge, which are found to be responsible for the higher uptake of hydrogen, through a dipole–dipole and change-induced dipole interaction. The binding energies of hydrogen on these systems were found to be in the range of 0.1 eV to 0.2 eV, which are ideal for the practical applications in a reversible system.

Tuning the Electronic and Magnetic Properties of Phosphorene by Vacancies and Adatoms

Srivastava, Pooja,Hembram, K. P. S. S.,Mizuseki, Hiroshi,Lee, Kwang-Ryeol,Han, Sang Soo,Kim, Seungchul American Chemical Society 2015 The Journal of Physical Chemistry Part C Vol.119 No.12

<P>We report a density functional theory (DFT) study regarding the effects of atomic defects, such as vacancies and adatom adsorption, on the electronic and magnetic properties of phosphorene (a two-dimensional monolayer of black phosphorus). A monovacancy in the phosphorene creates an in-gap state in the band gap of pristine phosphorene and induces a magnetic moment, even though pristine phosphorene is nonmagnetic. In contrast, both planar and staggered divacancies do not change the magnetic properties of phosphorene, although a staggered divacancy creates states in the gap. Our DFT calculations also show that adsorption of nonmetallic elements (C, N, and O) and transition metal elements (Fe, Co, and Ni) can change the magnetic properties of phosphorene with or without vacancies. For example, the nonmagnetic pristine phosphorene becomes magnetic after the adsorption of N, Fe, or Co adatoms, and the magnetic phosphorene with a monovacancy becomes nonmagnetic after the adsorption of C, N, or Co atoms. We also demonstrate that for O- or Fe-adsorbed monovacancy structure the electronic and magnetic properties are tunable via the control of charge on the phosphorene system. These results provide insight for achieving metal-free magnetism and a tunable band gap for various electronic and spintronic devices based on phosphorene.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2015/jpccck.2015.119.issue-12/jp5110938/production/images/medium/jp-2014-110938_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp5110938'>ACS Electronic Supporting Info</A></P>

New carbon allotropes in sp + sp³ bonding networks consisting of C₈ cubes

Wang, Jian-Tao,Chen, Changfeng,Mizuseki, Hiroshi,Kawazoe, Yoshiyuki The Royal Society of Chemistry 2018 Physical Chemistry Chemical Physics Vol.20 No.12

<P>We identify using <I>ab initio</I> calculations new types of three-dimensional carbon allotrope constructed by inserting acetylenic or diacetylenic bonds into a body-centered cubic C8 lattice. The resulting sp + sp<SUP>3</SUP>-hybridized cubane-yne and cubane-diyne structures consisting of C8 cubes can be characterized as a cubic crystalline modification of linear carbon chains, but energetically more favorable than the simplest linear carbyne chain and the cubic tetrahedral diamond and yne-diamond consisting of C4 tetrahedrons. Electronic band calculations indicate that these new carbon allotropes are semiconductors with an indirect band gap of 3.08 eV for cubane-yne and 2.53 eV for cubane-diyne. The present results establish new types of carbon phases consisting of C8 cubes and offer insights into their outstanding structural and electronic properties.</P>

Orthorhombic carbon oC24: A novel topological nodal line semimetal

Li, Zhen-Zhen,Chen, Jia,Nie, Simin,Xu, Lifang,Mizuseki, Hiroshi,Weng, Hongming,Wang, Jian-Tao Elsevier 2018 Carbon Vol.133 No.-

<P><B>Abstract</B></P> <P>We identify by <I>ab initio</I> calculations a stable three-dimensional carbon allotrope that constructed by inserting benzene rings into the carbon-carbon bonds in a previously reported oC8 carbon. This new carbon phase has a 24-atom orthorhombic unit cell in C m m m ( D 2 H 19 ) symmetry and thus termed oC24. Phonon mode analysis confirms its dynamical stable. Total-energy calculations show that it is energetically stable comparable with (5,5) carbon nanotube. Detailed electronic band calculations reveal that oC24 is a topological node-line semimetal with two mirror-inversion symmetric nodal lines that go through the whole Brillouin zone in bulk and a projected surface flat band around the Fermi level. The present results establish a new type of carbon phases and offer insights into their outstanding structural and electronic properties.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Strong chromate-adsorbent based on pyrrolic nitrogen structure: An experimental and theoretical study on the adsorption mechanism

Ko, Young-Jin,Choi, Keunsu,Lee, Soonjae,Jung, Kyung-Won,Hong, Seokwon,Mizuseki, Hiroshi,Choi, Jae-Woo,Lee, Wook-Seong Elsevier 2018 Water research Vol.145 No.-

<P><B>Abstract</B></P> <P>Chromate is considered a toxic contaminant in various water sources because it poses a risk to animal and human health. To meet the stringent limits for chromium in water and wastewater, pyrrolic nitrogen structure was investigated as a chromate adsorbent for aqueous solutions, employing a polypyrrole coating on carbon black. The characteristics of the adsorbent were analyzed by high-resolution transmission electron microscopy, energy-filtered transmission electron microscopy, and X-ray photoelectron spectroscopy. Chromate was adsorbed as both Cr(III) and Cr(VI). The chromate adsorption capacity increased (from 50.84 to 174.81 mg/g) with increasing amounts of pyrrole monomers (from 50 to 86%) in the adsorbent. The adsorption capacity was well-correlated with the pyrrolic nitrogen content (from 2.06 to 6.57 at%) in the adsorbent, rather than other types of nitrogen. The optimized adsorption capacity (174.81 mg/g in the equilibrium batch experiment and 211.10 mg/g at an initial pH of 3) was far superior to those of conventional adsorbents. We investigated the mechanism behind this powerful chromate adsorption on pyrrolic nitrogen via physical/chemical analyses of the pH-dependent adsorption behavior, supported by first-principles calculation based on density functional theory. We found that Cr(III) and Cr(VI) adsorption followed different reaction paths. Cr(III) adsorption occurred in two sequential steps: 1) A Jones oxidation reaction (JOR)-like reaction of Cr(VI) with pyrrolic N that generates Cr(III), and 2) Cr(III) adsorption on the deprotonated pyrrolic N through Cr(III)–N covalent bonding. Cr(VI) adsorption followed an alternative path: hydrogen-bonding to the deprotonation-free pyrrolic N sites. The pH-dependent fractional deprotonation of the pyrrolic N sites by the JOR-like reaction in the presence of chromate played an important role in the adsorption.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Polypyrrole-coated carbon black was employed as a chromate adsorbent. </LI> <LI> The Cr adsorption capacity was dependent on the amount of pyrrole monomer. </LI> <LI> Pyrrolic nitrogen induced reduction of hexavalent chromium to trivalent chromium. </LI> <LI> Trivalent chromium adsorbed to oxidized pyrrolic N by covalent bonding interactions. </LI> <LI> Hexavalent chromium adsorbed to pyrrolic N by hydrogen bonding interactions. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>