arXiv subjects

Norio Ota

Publications and source records attributed to Norio Ota.

At least 37 records · Page 2Linked to original sources

arXiv2017

Reproduction of Interstellar Infrared Spectrum of Reflection Nebula NGC2023 By A Hydrocarbon Pentagon-Hexagon Combined Molecule

Reflection Nebula NGC2023 shows specific interstellar infrared spectrum due to polycyclic aromatic hydrocarbon (PAH) in a wide wavelength range from 5 to 20 micrometer. By our previous quantum chemistry calculation, it was suggested that a molecule group having hydrocarbon pentagon-hexagon combined skeleton could reproduce ubiquitous interstellar infrared spectrum. In this paper, observed NGC2023 spectrum was compared in detail with such carrier candidates. First model molecule was di-cation (C23H12)2+ with two hydrocarbon pentagons combined with five hexagons. Observed strong infrared bands were 6.2, 7.7, 8.6, and 11.2 micrometer. Whereas, calculated strong peaks were 6.4, 7.5, 7.7, 8.5, and 11.2 micrometer. Observed weaker bands from 10 to 15 micrometer were 11.0, 12.0, 12.7, 13.5, and 14.2 micrometer, which were reproduced well by computed bands as 10.9, 12.0, 12.6, 13.6, and 14.0 micrometer. From 15 to 20 micrometer, observed 15.8, 16.4, 17.4, 17.8, and 19.0 micrometer were correlated with calculated 15.6, 16.5, 17.2, 18.2, and 18.8 micrometer. It should be noted that we could successfully reproduce interstellar infrared spectrum by applying a single molecule. Second model molecule was (C12H8)3+ with one pentagon combined with two hexagons. Again, observed strong bands at 6.2, 7.7, 8.6, 11.2 and 12.7 micrometer were successfully computed as 6.3, 7.4, 7.7, 8.6, 11.1, and 12.8 micrometer. It was concluded that by introducing hydrocarbon pentagon-hexagon combined ionized molecules, interstellar PAH oriented infrared spectrum could be successfully reproduced.

physics.atom-ph↗

arXiv2017

Astronomical chemical evolution from graphene to polycyclic aromatic hydrocarbon reproducing observed infrared spectrum

Interstellar ubiquitous infrared spectrum (IR) due to polycyclic aromatic hydrocarbon (PAH) was observed in many astronomical dust clouds. A capable astronomical chemical evolution path from graphene to PAH was studied based on the first principles calculation. Step 1 is a nucleation of nano-carbon after supernova by super-cooling at expanding helium sphere. As a typical model, graphene molecule (C )24 having coronene skeleton with seven carbon hexagons was tried.Step 2 is a proton sputtering and passivation on ejected graphene molecule. Slow speed proton with energy less than 4.3eV makes hydrogenation, Graphene molecule (C )24 was transformed to PAH (C24H12). Higher speed proton having sufficient energy larger than 18.3 eV could make a void in a molecule as like C23H12. Resulted structure was a combination of two carbon pentagons and five hexagons. Step 3 is photo-ionization of those molecules by high energy photon. Electrons are removed to make a molecule to cation. Model molecule (C23H12) became mono-cation (C23H12)+, di-cation (C23H12)2+ and so on. Typical energy difference between such cation was 6.5 and 10.8 eV. If the light source has a nature of black-body radiation, effective temperature will be 18000K ~ 24000K, which suggested that central light source star may have 4 to 7 times heavier than our sun. Finally, theoretical IR spectrum was obtained. Especially in case of (C23H12)2+, calculated emission spectrum revealed that among 13 major peaks, 11 peaks could correlate with ubiquitous observed IR one.

cond-mat.mes-hall↗

arXiv2016

Nitrogen Substituted Polycyclic Aromatic Hydrocarbon As Capable Interstellar Infrared Spectrum Source Considering Astronomical Chemical Evolution Step To Biological Organic Purine And Adenine

In order to find out capable chemical evolution step from astronomically created organic in interstellar space to biological organic on the earth, infrared spectrum of nitrogen substituted carbon pentagon-hexagon coupled polycyclic aromatic hydrocarbon was analyzed by the density functional theory. Ionization was modeled from neutral to tri-cation. Among one nitrogen and two nitrogen substituted NPAH, we could find good examples showing similar IR behavior with astronomically well observed one as like C8H6N1, C7H5N2, and C7H5N2. We can imagine that such ionized NPAH may be created in interstellar space by attacks of high energy nitrogen and photon. Whereas, in case of three and four nitrogen substituted cases as like C6H4N3 and C5H3N4, there were no candidate showing similar behavior with observed one. Also, IR of typical biological organic with four and five nitrogen substituted one as like purine and adenine resulted no good similarity with observed one. By such theoretical comparison, one capable story of chemical evolution of PAH in interstellar space was that one and two nitrogen substituted carbon pentagon-hexagon molecules may have a potential to be created in interstellar space, whereas more than three nitrogen substituted molecules including biological organic purine and adenine may not be synthesized in space, possibly on the earth.

physics.chem-ph↗

arXiv2015

Magnetic domain walls in nanostrips of single-crystalline $\mathrm{Fe}_4\mathrm{N}(001)$ thin films with fourfold in-plane magnetic anisotropy

We investigated head-to-head domain walls in nanostrips of epitaxial $\mathrm{Fe}_4\mathrm{N}(001)$ thin films, displaying a fourfold magnetic anisotropy. Magnetic force microscopy and micromagnetic simulations show that the domain walls have specific properties, compared to soft magnetic materials. In particular, strips aligned along a hard axis of magnetization are wrapped by partial flux-closure concertina domains below a critical width, while progressively transforming to zigzag walls for wider strips. Transverse walls are favored upon initial application of a magnetic field transverse to the strip, while transformation to a vortex walls is favored upon motion under a longitudinal magnetic field. In all cases the magnetization texture of such fourfold anisotropy domain walls exhibits narrow micro-domain walls, which may give rise to peculiar spin-transfer features.

cond-mat.mtrl-sci↗

arXiv2015

Asymmetric polycyclic aromatic hydrocarbon as a capable source of astronomically observed interstellar infrared spectrum

In order to find out capable molecular source of astronomically well observed infrared (IR) spectrum, asymmetric molecular configuration polycyclic aromatic hydrocarbon (PAH) was analyzed by the density functional theory (DFT) analysis. Starting molecules were benzene C6H6, naphthalene C10H8 and 1H-phenalene C13H9. In interstellar space, those molecules will be attacked by high energy photon and proton, which may bring cationic molecules as like C6H6n+ (n=0~3 in calculation), C10H8n+, and C13H9n+, also CH lacked molecules C5H5n+, C9H7n+, and C12H8n+. IR spectra of those molecules were analyzed based on DFT based Gaussian program. Results suggested that symmetrical configuration molecules as like benzene, naphthalene , 1H-phenalene and those cation ( +, 2+, and 3+) show little resemblance with observed IR. Contrast to such symmetrical molecules, several cases among cationic and asymmetric configuration molecules show fairly good IR tendency. One typical example was C12H83+, of which calculated harmonic IR wavelength were 3.2, 6.3, 7.5, 7.8, 8.7, 11.3, and 12.8 micro meter, which correspond well to astronomically observed wavelength of 3.3, 6.2, 7.6, 7.8, 8.6, 11.2, and 12.7 micro meter. It was amazing agreement. Also, some cases like C5H5+, C9H7+, C9H72+, C9H73+ and C12H82+ show fairly good coincidence. Such results suggest that asymmetric and cationic PAH may be capable source of interstellar dust.

astro-ph.GA↗

arXiv2015

Modeling astronomically observed interstellar infrared spectra by ionized carbon pentagon-hexagon molecules (c9h7) n+

Modeling a promising carrier of the astronomically observed polycyclic aromatic hydrocarbon (PAH), infrared (IR) spectra of ionized molecules (C9H7) n+ were calculated based on density functional theory (DFT). In a previous study, it was found that void induced coronene C23H12++ could reproduce observed spectra from 3 to 15 micron, which has carbon two pentagons connected with five hexagons. In this paper, we tried to test the simplest model, that is, one pentagon connected with one hexagon, which is indene like molecule (C9H7) n+ (n=0 to 4). DFT based harmonic frequency analysis resulted that observed spectrum could be almost reproduced by a suitable sum of ionized C9H7n+ molecules. Typical example is C9H7++. Calculated peaks were 3.2, 7.4, 7.6, 8.4, and 12.7 micron, whereas observed one 3.3, 7.6, 7.8, 8.6 and 12.7 micron. By a combination of different degree of ionized molecules, we can expect to reproduce total spectrum. For a comparison, hexagon-hexagon molecule naphthalene (C10H8) n+ was studied. Unfortunately, ionized naphthalene shows little coincidence with observed one. Carbon pentagon- hexagon molecules may play an important role as interstellar molecular dust.

physics.chem-ph↗

arXiv2015

Infrared spectra of methyl-, and nitrogen-modified void coronene; modeling a carrier of interstellar polycyclic aromatic hydrocarbon

Void induced coronene C23H12++ was suggested to be a possible carrier of the astronomically observed polycyclic aromatic hydrocarbon (PAH), which shows unique molecular structure with carbon two pentagons connected with five hexagons. Well observed astronomical infrared spectrum from 3-15 micron could be almost reproduced based on density functional theory. However, there remain several discrepancies with observed spectra, especially on 11-15 micron band weaker intensity. Observed 11.2 micron intensity is comparable to 7.6-7.8 micron one. Methyl-modified molecule C24H14++ revealed that calculated peak height of 11.4 micron show fairly large intensity up to 70-90% compared with that of 7.6-7.8 micron band. Also, nitrogen atom was substituted to peripheral C-H site of void coronene to be C22H11N1++. Pentagon site substituted case show 60% peak height. This molecule also reproduced well 12-15 micron peak position and relative intensity. Vibration mode analysis demonstrated that 11.3 micron mode comes from C-H out of plane bending. Heavy nitrogen plays as like an anchor role for molecule vibration.

physics.chem-ph↗

arXiv2015

Vibrational mode analysis of void induced coronene as a possible carrier of the astronomical aromatic infrared bands

Void induced di-cation coronene C23H12++ is a possible carrier of the astronomically observed polycyclic aromatic hydrocarbon (PAH). Based on density functional theory, multiple spin state analysis was done for neutral void coronene C23H12. Singlet spin state was most stable (lowest total energy). By the Jahn-Teller effect, there occurs serious molecular deformation. Point group D6h of pure coronene transformed to C2 symmetry having carbon two pentagons. Advanced singlet stable molecules were di-cation C23H12++ and di-anion C23H12- -. Molecular configuration was almost similar with neutral C23H12. However, electric dipole moment of these two charged molecules show reversed direction with 1.19 and 2.63 Debey. Calculated infrared spectrum of C23H12++ show a very likeness to observed one of two astronomical sources of HD44179 and NGC7027. Harmonic vibrational mode analysis was done for C23H12++. At 3.2 micrometer, C-H stretching at pentagons was featured. From 6.4 to 8.7 micrometer, C-C stretching mode was observed. In-plane-bending of C-H was in a range of 7.6-9.2 micrometer. Both C-H out-of plane bending and C-C stretching were accompanied from 11.4 to 14.3 micrometer. Astronomically observed emission peaks of 3.3, 6.2, 7.6, 7.8, 8.6, 11.2, 12.7, 13.5 and 14.3 micrometer were compared well with calculated peaks of 3.2, 6.5, 7.6, 7.8, 8.6, 11.4, 12.9, 13.5, and 14.4 micrometer.

physics.chem-ph↗

arXiv2014

Void induced molecule c23h12++ could reproduce the infrared spectrum (3 to 20 micron) of interstellar gas and dust

In order to find out a selected number of molecules to reproduce the infrared spectrum of interstellar gas and dust, model coronene molecules with void and charge have been computed using density functional theory. Among them, a single void induced cation C23H12++ have successfully reproduced a wide range spectrum from 3 to 20 micron of typical interstellar gas and dust. Well known astronoically observed emission peaks are 3.3, 6.2, 7.6, 7.8, 8.6, 11.2, 12.7, 13.5 and 14.3 micro meter. Whereas, calculated peaks of C23H12++ were 3.2, 6.4, 7.6, 7.8, 8.6, 11.4, 12.9, 13.5, and 14.4 micron meter. It should be noted that a single kind of molecule could reproduce very well not depending on the decomposition method using many polycyclic aromatic hydrocarbon (PAH) data. Such coincidence suggested that some astronomical chemical evolution may select a particular PAH. Molecular sructure of C23H12++ was dramatically deformed by the Jahn-Teller effect. There is a featured carbon skeleton having two pentagons connected to highly symmetrical five hexagons. Such unique structure brings above infrared mode.

astro-ph.GA↗

arXiv2014

Jahn-Teller Distortion and Multiple-spin-state Analysis of Single-atom Vacancy in Graphene-nano-ribbon

A single-atom vacancy defect and its array in graphene and graphite were considered to be one candidate carrying the room-temperature ferromagnetism. Applying density functional theory to a single-atom vacancy in graphene-nano-ribbon (GNR), a detailed relationship between the multiple-spin-state and the Jahn-Teller distortion was studied. An equilateral triangle of an initial vacancy having six unpaired electrons had distorted to isosceles triangle by the Jahn-Teller effect. Among capable spin-state of Sz=6/2, 4/2 and 2/2, the most stable one was Sz=2/2. Total energy was 15.6 kcal/mol lower (stable) than that of the initial one and a sum of spin density (magnetic moment) around one vacancy was 1.49 μB. Amazing result was obtained in case of Sz=4/2. Initial flat ribbon turned to three dimensionally curled one. There appears ferromagnetic spin distribution on GNR. Total energy was -15.5kcal/mol, which was very close to that of Sz=2/2. Such calculation suggested the coexistence of flat ribbon and curled ribbon by generating vacancies. Bi-layered AB stacked GNR was analyzed in case of α-site vacancy and also \b{eta}-site one. The most stable spin state was Sz=2/2 in both cases. These distorted vacancy triangle show 60 degree clockwise rotation from beta- to alpha-site, which is consistent with several experimental observations by using a scanning tunneling microscope.

cond-mat.mes-hall↗

arXiv2014

Magnetic Moment and Band Structure Analysis of Fe, Co, Ni-modified Graphene-nano- ribbon

Magnetic properties and band characteristics of graphene-nano-ribbon (GNR) modified by Fe, Co, and Ni were analyzed by the first principles DFT calculation. Typical unit cell is [C32H2Fe1], [C32H2Co1] and [C32H2Ni1] respectively. The most stable spin state was Sz=4/2 for Fe-modified GNR, whereas Sz=3/2 for Co-case and Sz=2/2 for Ni-case. Atomic magnetic moment of Fe, Co and Ni were 3.63, 2.49 and 1.26 μB, which were reduced values than that of atomic Hund-rule due to magnetic coupling with graphene network. There is a possibility for a ferromagnetic Fe, Co and Ni spin array through an interaction with carbon pi-conjugated spin system. By expanding a unit cell of Co-modified case as [C96H6Co3], ferromagnetic like spin state and ferrimagnetic like one were compared. It was concluded that ferromagnetic state was more stable magnetic state. Band calculations of Co-modified case show half-metal like structure with relatively large band gap (0.55eV) for up-spin, whereas small gap (0.05eV) for down-spin. This suggested a capability of spintronics application like a spin fiter.

cond-mat.mes-hall↗

arXiv2013

Ferromagnetic Order Analysis of Fe- and FeO-modified Graphene-nano-ribbon

Graphene-nano-ribbon (GNR) is very attractive for ultra-high density spintronics devices. For checking a capability of self-induced ferromagnetic order, Fe- and FeO-modified GNR were analyzed based on the density functional theory. Model unit cells were [C32H2Fe2] and [C32H2Fe2O2]. Calculated results show the most stable spin state to be Sz=8/2 in [C32H2Fe2], whereas Sz=6/2 in [C32H2Fe2O2]. Magnetic moment M of Fe in [C32H2Fe2] was 3.65μB, which could be explained based on the Hund-rule considering donated charge to carbon to be M*=3.67μB . There is a capability of ferromagnetic Fe spin array through an interaction with carbon π-conjugated spin system. There shows a long-range super-exchange order in [C32H2Fe2O2]. Optimized atomic configuration gave the typical 90 degree super-exchange coupling between Fe-3d and O-2p orbit. Magnetic moment of Fe by DFT was 2.58μB, whereas super-exchange model considering donated charge to oxygen gave an estimated magnetic moment to be 2.60μB. Sign of magnetic moment of Fe and O are all up-spin each other. We could expect ferromagnetic long-range-order. Band structure was analyzed in FeO-modified case, which suggested half-metal like behavior. We can expect several spintronics applications as like a spin filter.

cond-mat.mes-hall↗

arXiv2013

Stable Spin State Analysis of Fe, Co, Ni-modified Graphene-ribbon

Magnetic graphene-ribbon is a candidate for realizing future ultra high density 100 tera bit/inch2 class data storage media. In order to increase the saturation magnetization, first principles DFT analysis was done for Fe, Co, Ni-modified zigzag edge graphene-ribbon. Typical unit cell is [C32H2Fe1], [C32H2Co1] and [C32H2Ni1] respectively. Most stable spin state was Sz=4/2 for Fe-modified case, whereas Sz=3/2 for Co-case and Sz=2/2 for Ni-case. Magnetic moment of Fe,Co, and Ni were 3.63, 2.49 and 1.26 μB, which can be explained by the Hund-rule considering charge donation to neighboring carbons. Band calculation shows half-metal like structure with a large band gap (in Co-case, 0.55eV) for up-spin, whereas very small gap (0.05eV) for down-spin, which will be useful for many featured application like information storage, spin filter and magneto-resistance devices. Dual layer Fe-modified ribbon shows a tube like curved structure, which may suggest a carbon nanotube creation by Fe catalyst.

cond-mat.mes-hall↗

arXiv2012

Design of Magnetic Graphene-ribbon for 100 Tera-bit/inch2 Information Storage Media

Magnetic graphene-ribbon is a candidate for realizing future ultra high density 100 tera bit/inch2 class data storage media. Multiple spin state analysis was done based on the density function theory. A typical model was a super cell [C80H7] which having bare (radical) carbons on one side zigzag edge, whereas mono hydrogenated on another side. Optimizing atomic configuration, self consistent calculation demonstrated that a total energy of the highest spin state is more stable than that of lower one, which came from exchange coupling between carbons. This analysis suggested a capability of designing magnetic data track utilizing such chemically edge modified graphene ribbon. In order to increase areal magnetization density, bilayer and quadri-layer graphene-ribbon model were analyzed. Detailed calculation resulted that also the highest spin state is the most stable one. Multiplying the layer numbers is effective way to realize and enhance strong magnetism.

cond-mat.mes-hall↗

arXiv2011

Magnetism of Edge Modified Nano Graphene

In order to study a magnetic principle of carbon based materials, multiple spin state of zigzag edge modified graphene molecules are analyzed by the first principle density functional theory to select suitable modification element. Radical carbon modified C64H17 shows that the highest spin state is most stable, which arises from two up-spin's tetrahedral molecular orbital configuration at zigzag edge. In contrast, oxygen modified C59O5H17 show the lowest spin state to be most stable due to four spins cancellation at oxygen site. Boron modified C59B5H22 have no π-molecular orbit at boron site to bring stable molecular spin state to be the lowest one. Whereas, C59N5H2 have two π-electrons, where spins cancel each other to give the stable lowest spin state. Silicon modified C59Si5H27 and Phosphorus modified C59P5H22 show curved molecular geometry due to a large atom insertion at zigzag site, which also bring complex spin distribution. Radical carbon and dihydrogenated carbon modification are promising candidates for designing carbon-based magnetic materials.

cond-mat.mes-hall↗

arXiv2011

Magnetic Counting Rule of Radical Carbon Edge Nano Graphene

In order to explain room-temperature ferromagnetism of graphite-like materials, this paper offers a new magnetic counting rule of radical carbon zigzag edge nano graphene. Multiple spin state analysis based on a density function theory shows that the highest spin state is most stable. Energy difference with next spin state overcomes kT=2000K suggesting a room-temperature ferromagnetism. Local spin density at a radical carbon shows twice a large up-spin cloud which comes from two orbital with tetrahedral configuration occupied by up-up spins. This leads a new magnetic counting rule to give a localized spin Sz=+2/2 to one radical carbon site, whereas Sz= -1/2 to the nearest carbon site. Applied to five model molecules, we could confirm this magnetic counting rule. In addition, we enhanced such concept to oxygen substituted zigzag edge occupied by four electrons.

cond-mat.mes-hall↗

arXiv2011

Asymmetric graphene model applied to graphite-like carbon-based ferromagnetism

Several experiments have recently found room-temperature ferromagnetism in graphite-like carbon based materials. This paper offers a model explaining such ferromagnetism by using an asymmetric nano-graphene. Our first typical model is C48H24 graphene molecule, which has three dihydrogenated (-CH2) zigzag edges. There are several multiple spin states competing for stable minimum energy in the same atomic topology. Both molecular orbital and density function theory methods indicate that the quartet state(S=3/2) is more stable than that of doublet (S=1/2), which means that larger saturation magnetization will be achieved. We also enhanced this molecule to an infinite length ribbon having many (-CH2) edges. Similar results were obtained where the highest spin state was more stable than lower spin state. In contrast, a nitrogen substituted (-NH) molecule C45N3H21 demonstrated opposite results. that is, the lowest spin state(S=1/2) is more stable than that of highest one(S=3/2), which arises from the slight change in atom position.

cond-mat.mes-hall↗

arXiv2011

Asymmetric nano graphene model applied to graphite-like room-temperature ferromagnetism

Room temperature ferromagnetic materials composed only by light elements like carbon, hydrogen and/or nitrogen, so called carbon magnet, are very attractive for creating new material categories both in science and industry. Recently several experiments suggest ferromagnetic features at a room temperature, especially in graphite base materials. This paper reveals a mechanism of such ferromagnetic features by modeling nanometer size asymmetric graphene molecule by using both a semi-empirical molecular orbital method and a first principle density function theory. Asymmetrically dihydrogenated zigzag edge graphene molecule shows that high spin state is more stable in total molecular energy than low spin state. Proton ion irradiation play an important role to create such asymmetric features. Also, nitrogen contained graphite ferromagnetism is explained by a similar asymmetric molecule model.

cond-mat.mes-hall↗