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OAtube Nanotechnology 1, 1009 (2008)

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Information about OAtube Nanotechnology 1, 1009 (2008)
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Published on October 29, 2008

Author: oatube

Source: authorstream.com

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Slide 1: Freezing and melting behavior of Gallium encapsulated in carbon nanotubes Zongwen Liu*, Simon P. Ringer* & Yoshio Bando** *The Australian Key Centre for Microscopy and Microanalysis The University of Sydney, NSW 2006, Australia **Advanced Materials Laboratory, National Institute for Materials Science Tsukuba, Ibaraki 305-0044, Japan Ga confined in Carbon nanotubes (CNTs) : Ga confined in Carbon nanotubes (CNTs) Overview In this presentation, it is demonstrated that when Ga is encapsulated in CNTs, it remains liquid far more lower than the melting point of its bulk form. upon cooling it solidifies either in -phase at or in -phase rather than the common -phase . when the confined Ga freezes, it has unique orientation relationships relative to the CNTs. Physical properties of Ga : Physical properties of Ga (a) melting point: 29.78 oC (b) ice-type element: expands 3.1% on solidifying (c) low vapor pressure even at high temperature Crystallography of Ga : Crystallography of Ga Crystal structures (a) stable form at normal conditions: -Ga (Ga-I) (b) two other phases stable at high pressure: Ga-II, a bcc structure Ga-III, a fct structure. (c) high pressure bct to fcc transition (d) metastable phases: , , , and  Crystallography data of -, -, and -Ga : Crystallography data of -, -, and -Ga -Ga -Ga -Ga Symmetry orthorhombic monoclinic orthorhombic Space group Cmca C2/c Cmcm a=4.519 a=2.766 a=10.593 Lattice b=7.660 b=8.053 b=13.523 parameters (Å) c=4.525 c=3.332 c=5.203 =92o Atoms/unit cell 8 4 10 Density 0.43 0.45 0.45 Melting point 29.78 oC -16.63 oC -35.6 oC CNTs encapsulated with Ga : CNTs encapsulated with Ga TEM images showing CNTs encapsulated with Ga Slide 7: Ga: catalyst Synthesis of CNTs confined with Ga Freezing and melting of Ga encapsulated in a CNT : Freezing and melting of Ga encapsulated in a CNT Freezing (solidification) at -80 oC (-phase) Volume decrease upon freezing (~1.1%) Melting at -20 oC 21oC - 40oC (a) (b) (c) (d) (e) -80oC -20oC 21oC 100nm Zongwen Liu et al, Phys. Rev. Lett., 93, 095504 (2004). Thermal expansion of Ga encapsulated in a CNT : Thermal expansion of Ga encapsulated in a CNT Thermal expansion coefficient: 0.1008x10-3 For bulk Ga (30-977oC): 0.1015x10-3 Electron irradiation damage : Electron irradiation damage (a) (b) (c) The shrinkage of the CNT diameter upon electron irradiation: (a) Image taken before cooling (b) After 5 cycles of freezing and melting (c) After 10 cycles of freezing and melting Electron irradiation damage : Electron irradiation damage Effect of electron beam irradiation (a) Weak beam (b) Strong beam Freezing and melting of -Ga and -Ga : Freezing and melting of -Ga and -Ga (a) Liquid state. (d) Solid state. (b) Freezing of -Ga at -70 oC (top). (e) -Ga melts -21 oC. (c) Freezing of -Ga at -80 oC (bottom). (f) -Ga melts at -20 oC. 21oC - 40oC -70oC -20oC 21oC Electron diffraction analysis : Electron diffraction analysis - 40oC -70oC (a)  A CNT with two Ga columns (b) and (c)  from upper column, [010] and [123] of -Ga. (d) and (e)  from lower column, [310] and [510] of -Ga. Measured and calculated plane spacings of - and -Ga : Measured and calculated plane spacings of - and -Ga (020) 3.951 4.027 (001) 3.267 3.332 -Ga (021) 2.518 2.566 (-130) 1.909 1.926 (1-50) 1.356 1.392 (200) 5.160 5.296 (11-1) 4.321 4.414 -Ga (002) 2.519 2.601 (4-20) 2.427 2.466 (3-31) 2.412 2.452 Planes Spacing (Å) Measured Calculated * The difference between measured and calculated values is only about 1.9% Melting of Ga encapsulated in CNTS : Melting of Ga encapsulated in CNTS Melting of -Ga Bulk form: -16.3 oC Confined in CNTS: -20 oC  close to bulk 2. Melting of -Ga Bulk form: -35.6 oC Confined in CNTS: -20 oC  super heating effect 3. Factors that could affect the melting point a) interaction between Ga and the wall of the CNT b) high vacuum in TEM c) a new kind of CNT confinement effect Freezing of Ga confined in CNTs : Freezing of Ga confined in CNTs 1. When solidifies, the confined Ga has unique orientation relationships relative to the CNT 3. The confined Ga freezes as a single crystal irrespective of the shape of the carbon nanotube. 2. For -Ga, it has been determined either the (011) plane or the (061) plane of the -Ga aligns parallel to the axis of the carbon nanotube. A new confinement effect : A new confinement effect HRTEM image of -Ga in [100] orientation. The arrowed 0.256 nm is the (021) spacing. The arrowed reflections in the diffraction are from carbon (002). Summary : Summary When Ga is encapsulated in CNTS it remains liquid down to -70 or -80 oC. 2. Upon freezing the confined Ga can crystallize in either -phase or -phase rather than the common -phase. 3. The confined Ga freezes as a single crystal irrespective of the shape of the carbon nanotube. 4. The solidified -Ga maintains two unique orientation relationships relative to the axis of the CNT. 5. Both the -Ga and the -Ga melt at around -20 oC.

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