New functionalities in abundant element oxides: ubiquitous element - PowerPoint PPT Presentation

New functionalities in abundant element oxides: ubiquitous element strategy Japan-EU Workshop “Substitution of Critical Raw Materials” @ EU Japan Office(Nov.21) μ m -scale nm -sized structure m -sized structure Hideo HOSONO Tokyo Institute of Technology, Yokohama, Japan

Research on C12A7 led to a Science & Technology Policy “Element Strategy for Sustainable society” National Policy (Started from 2008) Ubiquitous Element Strategy Clark Number Function Structure Element Order Element 1 1 1 1 O O O O size 2 2 2 2 Si Si Si Si charge 3 3 3 3 Al Al Al Al nanostructure orbital 4 4 4 4 Fe Fe Fe Fe interface spin 5 5 5 5 Ca Ca Ca Ca defect theoretical 6 6 6 6 Na Na Na Na measuremen t 7 7 7 7 K K K K Unconventional Valence state 8 8 8 8 Mg Mg Mg Mg 9 9 9 9 H H H H 10 10 10 10 Ti Ti Ti Ti

Electro-active materials made from 3 Structural Materials High Performance Transistor Proposal of Transparent Amorphous Oxide Semicoductors (1995) Fabrication of transparent flexible transistor(2004, Nature) 70-inches , UD, 240Hz LCD driven by TAOS-TFT Arrays (Samsung@ FPD Int ’10) Transparent metal from Cements Transparent p-type semiconductor O O Focusing on Built ‐ in nanostructure F F La-O La-O In 12CaO ・ 7Al 2 O 3 (1998) layer layer La La molten metallic electride e - e - Fe-As Fe-As Fe Fe (2011, Science) layer layer As As Conversion toTransparet metal. (2004,Science) Discovery of a new high Tc Supercond. since 1986 Breaking a common sense that Iron is the last element Highest Tc except Cuprates, “2 nd fever” for superconductivity （ 2008,JACS & Nature)

SHARP has announced adoption of a-IGZO-TFTs for mobile LCDs (June 3, 2011) Introduction of IGZO-TFT to Kameyama-2 factory Pres. Katamaya Production expansion tablet high precision, high quality of mobile LCD computer terminal ultra low power assumption JST issued parent license smart ( non-exclusive) of I GZO-TFT phone o Sam sung EL 2010 2011 2012 a-IGZO TFTs are going to apply to iPad3 with high resolution .

12CaO ∙ 7Al 2 O 3 (C12A7) powder single crystal • A constituent of alumina cements Mp. 1415 ºC • Large band gap ~7 eV • Cubic (a = 1.199 nm, I43d) Unit cell: Ca 24 Al 28 O 66 = [Ca 24 Al 28 O 64 ] +4 + 2O 2 – • 12 Cages Free Oxygen Ions 6 × 10 21 cm –3 1 × 10 21 cm –3 Unit cell Al O 1.199 nm Ca Densely Packed Fast Oxygen I on Conductor Sub-nano-sized Cages

Electronic Structure of C12A7 6 Conduction Band Wave functions Evac (Framework) confined in cages 4 WF=2.4eV Cage Conduction Band 2 Energy (eV) 0 tunneling O 2 p ( Free Oxygen ) -2 Valence Band (Framework) -4 Ζ Α Μ Γ Ζ Ρ Ξ Γ k PRL(2003), PRB(2005), Nanolett(2007), Adv.Mat (2007)

Cage Conduction Band Cage conduction band Hard XPS Fermi edge Adv.Mater. (2007)

Electron-doping to C12A7 [Ca 24 Al 28 O 64 ] 4+ ( 2O 2– ) + Ti → [Ca 24 Al 28 O 64 ] 4+ ( 4e – ) + TiO X (Max 2.3x10 2 1 cm -3 ) Free O 2- cage Ti TiO X (metallic) (insulating) e – Out-diffusion of free O 2- Science(2003), Nanolett(2007)

Metal – Insulator Transition Metal composed of typical insulators, lime and alumina ! 1.5x10 3 Scm -1 @RT 2x10 21 cm -3 Band Conduction Nc = ~1 × 10 21 cm –3 Metal – Insulator Transition electron Hopping Conduction concentration In cages 3x10 19 cm -3 Polaron : electron localized by lattice distortion Nano Lett Lett. 2007 . 2007 Nano σ = ∼ 10 -10 Scm -1

Metal-Superconducting Transition in C1 2 A7 :e - single crystals FZ -grown single crystal 100% 100% First s-metal superconductor at P= 1atm JACS.( ２００７ )

Work function of C12A7:e - ~ 2.4 eV Al Mg O-LED Li 2.9 Ca Na Ba Sm LaB 6 2.7 E-gun Sr Alkaline Eu C12A7:e - Alkaline earth K 2.3 Rare earth 2.2 Rb 2.1 Cs 4 1 2 3 Work function (eV)

Unique Properties of C12A7:e - metal : small workfunction and chemical inertness 2.4eV WF= (cage conduction band) WF Li(2.9),Na(2.7),K(2.4), Mg(3.7),Ca(2.9) Adv.Mater(2007)

C12A7: e- C12A7 : O - C12A7 world - C12A7: O 2 Low work function but stable 2x10 21 cm -3 2x10 21 cm -3 Strong oxidation power 3x10 19 cm -3 3x10 19 cm -3 Energy (eV) 6 C12A7: H - Field e-emitter 4 2 MI& MS transition single cryst. 0 ④ ④ ⑤ ⑤ H - -2 ① ① -4 ⑥ ⑥ ② ② Ζ Α Μ Γ Ζ Ρ Ξ Γ Cathode for OLED ③ ③ マスク thin film Unique band structure Encaged ReRAM Surface electron Ca O in water Al H H Ar Ar Ar C O 絶縁性 C12A7:H - Melt&Glass H HO OH UV(e-beam)-induced 1,2-diol Insulator-conductor conversion reagents for organic reaction

Activation of Inert chemical species at C12A7 electride surface � High density of electron trapped cages ~10 13 /cm 2 � Low work function ~2.4 eV Activation by electron transfer Is it possible? Low work function electron

STM Observation on C12A7:e - surfaces Ex Situ I-V characteristics

Enlarged View (110) (111) (100) 1 nm 1 nm 1 nm 3x3 nm, +2.5 V, 0.05 nA atomistic order 0.2 ~ 0.3 nm ~ 0.2 nm ~ 4 nm 2 ~ 7 °

Surface model for (100) Bulk truncated Cage conserved Atom density Thermal stability Conductivity Cage Open mouths : Not observed by experiments conserved

STM Images vs. Cage conserved model (110) (111) (100) X: Ca White : Defect Black : Adatom ACS Nano (2011)

Can we obtain solvated electron in high temperature oxide melt /glass? Liquid ammonia M ‐ I transition Solvated cation Solvated electron

Molten state of C12A7 electride : metallic conduction C12A7:O 2 − Melt C12A7:e − Melt Ionic conducting Metallic conducting Transparent Strongly Colored Concentration of Solvated electrons ~10 21 cm -3 The photo was taken through a color filter Science, 333, 71 (2011)