Chutia Arunabhiram

English

博士学位論文の要旨及び審査結果の要旨 (Summary of Thesis(DR))othe

Chutia, Arunabhiram

Tohoku University Repository (TOUR) / 東北大学機関リポジトリ

Molecular Morphological Influence of GrapheneRelated Carbon Materials on Their Electronicand Electrical Properties:A Theoretical Study(グラフェン関連カーボン材料の分子構造および電子・電気特性に関する理論研究)著者 Chutia Arunabhiram号 53学位授与番号 4033URL http://hdl.handle.net/10097/42447ちゅて いあ あ るなび らん氏 名ChutiaArunabhiram授 与 学 位 博士(工 学)学 位 授 与 年 月 日 平成20年9月11日学位授 与の根拠法規 学位規則第4条 第1項研究科,専 攻の名称 東北大学大学院 工学研究科(博 士課程)応 用化学専攻学 位 論 文 題 目MOIecUlarM¢⇔holq暫副lr血㎜ceofGrapheneRelatedCabonMa㎞alsonllieirEleCtronicaridElectricalPlr'operties:ATheoreticalStudy(グラフェン関連カーボン材料の分子構造お よび電子 ・電気特性に関する理論研究)指 導 教 員 東北大学教授 宮本 明論 文 審 査 委 員 主査 東北大学教授 京谷 隆 東北大学教授 浅井 圭介東 北大学教授 久保 百司論 文 内 容 要 旨Chapter 1  Introduction Experimental and theoretical studies in the past have  provided a  treasure of  information about he electronic and electrical properties ofwell  structured graphene r lated carbon materials (GRCMs) such as  graphite,  fullerenes and carbon anotubes. However more detailed studies are required for GRCMs with poor  crystallinity such as carbon blacks, activated carbon, graphite oxide,  soot, carbon fibers etc. This is because they have high values of  industrial pplication  such as in electronic components, cables, electrodes, lectrode additives, tires etc. but, their  structure and the basic understanding of the  functionality of these materials have not been achieved fully [1]. In the present investigation a theoretical study is presented with the motivation tocomprehend the influence ofchemical morphology on the electronic and  electrical properties of GRCMs. Chapter 2 Computational Methods Table 1. Binding  energy and bond population of bonding    A new method  was  developed by combining and  non-bonding atoms obtained from UA-QCMD and  tight-binding (TB) method with molecular dynamics method DFT to investigate he electronic and electrical properties of  .    Properties UA-QCMD DFT  GRCMs. This method is ten million times faster than the .                                       Binding Energy  (eV) -8.82 -8.12  conventional first-principles  methods. In this new Bond population methodology combined tight-binding quantum chemical Bonding atoms 1.06 1,09 calculations and molecular dynamics  (MD) simulations Non-bonding  atoms -0.09 -0.17  were  carried out, in this methodology first ight-binding method isemployed toderive potential parameters to be used for MD simulations. Other theoretical methods used for this study are density functional theory  (DFT) and time-dependent  DFT. Chapter 3 Validation of  Methodolou and Molecular  Modeline  Prior to the investigation  the electronic and  electrical  properties of GRMCs the validity of the newly developed Ultra Accelerated Quantum Chemical Molecular Dynamics (UA-QCMD) method was  checked. For  validating this methodology a graphite structure with 64 atoms was considered and  after the UA-QCMD calculations various parameters such as contribution of  electrons ins and p orbitals, bond populations and binding energy was compared with DFT results (see Table 1). This validated the newly derived  potentials for the MD simulations. Cha er 4 Influence of Cluster Size of Gra  I hene Sheets on  Electronic and Electrical Carbon Materials  Electrical conductivity of GRCMs is dependent on several factors such as conductivity of individual particles, degree of  contact  among the particles tc  [2]. In this tudy first he highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO)  energies, HOMO-LUMO energy gap, chemical h rdness and chemical  softness of GRCM models were investigated, which provided an insight into their electronic and electrical properties. Onestimation of electrical conductivity of these  models, as shown in  Figure 1, it was found that with the GI   104 c/5  tab  8  8  io-Drties of  Graphene Related x x XGRCM  1  GRCM 2  GRCM 3  GRCM 4  GRCM 5  GRCM 6   (44) (54)  (62) (90) (106) (260)  {GRCM [model  number  (n=1-6)]  (number  of  atoms)}  Figure 1  Electliail  ocnductivity of wrsusystemsincrease in cluster size the electrical conductivity significantly  increased.  Further, itwas seen that on stacking the basic  structural  units the electrical conductivity was  further increased. The basic reason for the enhanced electrical conductivity can be attributed to the increased number of  TE conjugations with cluster size or  ir-stackings of the BSUs. This work provided some of the fundamental explanations governing  the electronic and electrical properties of GRCMs at atomistic level. Chanter 5  Influence of Chemical  Morpholoev of Graphene Sheets on the Electrical  Properties of Graphene RelatedCarbon Materials  In chapter 5 for  the first time a theoretical study on the influence of chemical morphology on the electrical  properties  of-OHand  -SH modified graphene r lated carbon materials was carried  out It was seen that in the layered graphene models generated by  5,  stacking BSUs (see  Figure 2) the energy gap shows a decreasing trend with increasing number of stacked layers.  However, it is dependent on  AAA  stacking (where all atoms in the consecutive layers are above one another) or ABA  stacldng (where half of the atoms inthe consecutive layers are directly above the center of the hexagonal ring and half directly over each other), patterns and on2.0  1.8 1.6 1.4 1.2  1.0 0.8 0.6 0.4 0.2 0.0-\c- - -1   \ 1 ---.---  G(011) AAA  stacking  ---6--  G(SED AAA stacking  ---.--  0(  OH) ABA stacking  —10--G(SH) ABA stackingki I 2 3 4                                                                 Number of  layers  Figure 2 Energy  gap  versus number  of -OH and  -SH  modified   grapbene  (G)  layers  inAAA  or  ABA stacking patterns the interactions between the stacked layers. For the oxygen modified graphenes the electronic properties were seen to be independent of the stacking patterns of the graphenes due to the higher electronegative  nature of the oxygen atoms. In the sulfur modified graphenes the electronic and  electrical properties are dependent on the stacking patterns. The  reason for the  anomalous behavior f sulfur modified graphenes is understood in terms of the interaction between the it-electron rich beds. It  was een that by engineering the interlayer distances between the graphene layers the electronic and henceforth e  electrical  Properties of graphene r lated carbon materials can be altered.  Estimation of electrical  conductivity for largermodels at different densities also revealed that electrical conductivity of the functionalized graphenes is dependent on the interlayer  distances. Chapter 6 Influence of Chemical  Morpholou  of  Gra hene Sheets of Gra hene Related Carbon Materials as CatalSupport for Pt Catalysts To prepare and use heterogeneous catalysts deeper understanding ofthe nature of  support and metal oading is required. In  chapter  6, the  adsorption of Pt4 catalysts on  functionalized graphenes was  first investigated. It was  theoretically shown that the adsorption of Pt on the graphene related carbon  materials with oxygen containing roups are NUMMI'  01  -kiri  groups dependent onthe concentration of these groups  (Figure 3). This agrees Figure 3 Adsciption  e ergy  of Pt  on the  ideal  GRCM model with the  experimental findings  [2]. The fundamental reason  governing with the  increase in the  -OH  groups the dependence of the favorable Ptadsorption the concentration of oxygen containing group is due the electron density in the pristine graphene sheet.  Higher  concentration of oxygen containing groups results in the depletion of electron density  which causes weakening of the anchoring capability of the n-sites towards Pt catalysts and results in the increase of adsorption  energy. Since small or no HOMO-LUMO gap represents higher reactivity an analysis on HOMO-LUMO gap and chemical softness of all  these systems was also carried out. It was clearly seen that adsorption of Pt4 cluster on pristine graphene with an optimum number  of—OH groups had the least energy gap and highest chemical softness among all the systems implying a high  reactivity. This study provided the first theoretical evidence of the influence of chemical morphology on the adsorption Pt catalyst on graphene related materials.  Chapter 7 Electronic and  Electrical  Properties of 1-D  ()manic Chains and their  Composites of Rolled  GranheneSheets Table 2. Energy gap and electrical conductivity of The first  part of this  investigation was focused on the study of the electronic and electrical  properties of  1D linear organic chains namely alkenes with general  formula  Cnt.42 with n  =  2,  4, 8, 10, 14 and 16.  It was seen that as the number of carbon atoms of these linear  1D organic chains  increased they attained  semi-conducting behavior. This was due to  the increase in  the number of  it-electrons in the systems.  This showed that sufficiently longer  1E) organic  Ci,H„4-2 systems would behave like semiconductors. A case study on the effect of doping onthese  systems was carried out with reference to  C81-110  system. Itwas Figure 4  Energy lewl diagram  showing energy  harrier  forseen that upon doping by bromine the conductivity of  C81-110 system  the  f°"114(311  4(7, 0)cNT-c4145  cemNsites was  -109 times higher than the undoped  C8Hio  system (see Table 2). In this study for the first time quantitative  estimation felectrical conductivity of all the  C„F12,1+2 systems were reported  theoretically.  This work was further extended to the  investigation of composite materials of  Ciilin+-2  (n=4) and (7,0)  CNT. First he reaction mechanism for the formation f (7,0) CNT-C4H5 composite was carried out and a free radical reaction mechanism was proposed.  TS calculation showed that energy barrier for the  reaction is -3.34  kcal/mol (Figure 4). Finally, a comparative study on the electronic and  electrical properties of  C4H6,  (7,  0)  CNT and (7, 0)  CN'T-C41-15 was carried  out  It was hown that the electrical onductivity of the  (7,  0)  CNT-C4H5 has an improved conductivity over both C4H6 and  (7,  0)  CNT systems.  This study provided theoretical evidences that he electrical onductivity of CNTs can be tailored by grafting  1Dorganic chains to  it. Chapter 8 Summary and  Conclusions   The present investigation hascontributed o the science of  GRCMs which reveals the fundamental aspects determining their electronic and electrical properties. This study also contributes to the  chemistry of Pt adsorption  GRCMs providing theoretical evidence forthe first ime about the importance of oxygen containing  groups in  carbon materials s catalysts upport  Furthermore, newcomposites materials of CNT-alkene systems were also proposed as a candidate formodifying electrical properties of  CNT. This study has paved the way for a new  field of computational  chemistry concerning thestudy of GRCMs. References:  [1] Nakada etal. Phys.  Rev. B  1996,  54, 17954, [2] Coloma et al.  Langmuir 1994, 10, 750, [3] Gavin et al. J.  Chem.  Phys.  1978,  68,  522.論文審査結果の要旨本論文は、グラフェン関連カーボン材料の分子構造および電子 ・電気特性を理論的に明らかにすることを 目的 として行われた。本論文はrMolecularMorphologicalInflue皿ceofGrapheneRelatedCarbonMaterialsontheirElectronicandElectricalProperties:ATheoreticalStudy(グラフェン関連カーボン材料の分子構造および電子 ・電気特性に関する理論研究)」と題 し、以下の8章 か らなる。第1章 では、グラフェン関連 カーボン材料の産業上における重要性について概説 した後に、本論文で対象と したグラフェン関連 カーボン材料の応用例 と求められる機能に関する理解の現状について述べ、本論文の目的を明確に している。第2章 では・本論文で用いた手法について説明 している。具体的には、独 自のTight'Binding理論に基 づ く量子分子動力学法 と古典分子動力学法を組み合わせた量子論に基づ く分子動力学法 について述べている。また・妥当性の検証などに用いた密度汎関数法および時間依存密度汎関数法 についてその理論 を詳述 している。第3章 では、Tight・Bindhlg量子分子動力学法に用いられるパラメータの妥当性の検証および分子モデ リングにっいて述べている。'15ght'Binding量子分子動力学法のパラメータは、Tight・Binding量子分子動力学法により計算 された原子の電荷や結合エネルギーを密度汎関数法 によるそれ らの値 と比較す ることで検証 した。第4章 で は、 グ ラフ ェンシー トのクラ スターサ イズが電子状 態や電気特 性 に与 え る影響 をTight・Binding量子分子動力学法 に基づき調べている。グラフェンシー ト中のベンゼ ン環の数の増加 とともに電気伝導特性が対数的に増加することが理論的に示された。さらに、グラフェンシー トを積層することで電気伝導性が向上することも理論的に明らかにされた。第5章 では、グラフェン関連化合物の電気特性に与える化学組成の影響を調べ る目的で、グラフェンシー ト末端 をヒドロキシル基およびチオール基で修飾 した積層 カーボン材料の電気特性を調べている。具体的には、それぞれの修飾グラフェンシー トの異なる積層構造における電気特性を調べ、積層媾造 ・化学修飾 と電気特性の関係 を明 らかにすることに成功 している。第6章 では、グラフェン関連カーボン材料の固体高分子形燃料電池の電極触媒担体 としての応用に焦点を絞 り、白金触媒とグラフェンシー トとの相互作用を電子 レベルで調べている。さらに、エタノールを燃料とした際の白金上での酸化反応について量子論に基づく解析を行 っている。第7章 では、アルキル鎖の電気特性に与える臭素 ドー ピングの影響を理論的に明らかにすることに成功 している。さらに、アルキル鎖 とカーボンナノチューブとの複合材料系の電気特性について も調べてお り、カーボンナノチューブの電気特性がアルキル鎖の修飾により制御可能であることを示すことに成功 している。第8章 は、本論文の総括である。以上、本論文は、量子論 に基づ く新規手法を活用す ることで、従来定量的理解が困難であったグラフェン関連化合物の電気特性に関 して電子 レベルでの新規知見を得ることに成功 している。よって,本 論文は博士(工学)の学位論文として合格と認める。94

Molecular Morphological Influence of Graphene Related Carbon Materials on Their Electronic and Electrical Properties:A Theoretical Study (グラフェン関連カーボン材料の分子構造および電子・電気特性に関する理論研究)

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Molecular Morphological Influence of Graphene Related Carbon Materials on Their Electronic and Electrical Properties:A Theoretical Study (グラフェン関連カーボン材料の分子構造および電子・電気特性に関する理論研究)

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