Nanostructures: scaling relation, metrology, and transport dynamics

IV-9: Nanostructures: scaling relation, size dependency, and transport dynamics

Chang Q. Sun (6790 4517),
Chang M. Li (6790 4485), and Sean Li (Materials/UNSW)
School of EEE, NTU, Singapore 639798
E-mail: ecqsun@ntu.edu.sg; URL: http://www.ntu.edu.sg/home/ecqsun/

Abstract
This talk presents a systematic understanding of the nature behind the unusual behavior of a nanosolid, and a surface as well, in mechanics, thermodynamics, acoustics, optoelectronics, magnetism, dielectrics, atomic diffusivity and chemical reactivity towards predictable design and controllable growth of nanostructured materials. A bond order-length-strength (BOLS) correlation mechanism has been developed, which has enabled the tunability of a variety of properties of a nanosolid in connection with surface to be consistently predicted and experimentally verified.

The BOLS correlation indicates that the coordination number (CN) imperfection of an atom at site surrounding a defect or in the surface skin causes the remaining bonds of the lower-coordinated atom to contract spontaneously. The spontaneous bond contraction is associated with bond-strength gain or atomic potential well deepening, which localize electrons and enhance the density of charge, mass, and energy in the relaxed region. The enhancement of energy density in the relaxed region perturbs the Hamiltonian and the associated properties such as the band-gap width, core-level energy, Stokes shift (electron-phonon interaction), and dielectric susceptibility. On the other hand, bond order loss lowers generally the cohesive energy of the lower-coordinated atom from the value of an atom with full CN, which dictates the thermodynamic process such as self-assembly growth, atomic vibration, thermal stability, and activation energies for atomic dislocation and diffusion. Consistency between predictions and observations evidences the enormous impact of atomic CN imperfection to the low-dimensional and disordered systems, including surface, amorphous and nanosolid states, and the validity, universality, and essentiality of the BOLS correlation.

Future direction includes (i) nanoscopic study for information such as single energy level of an isolated atom and dimer vibration frequency, etc, and (ii) Transport dynamics at the nanometer regime and, (iii) predictable design and controllable fabrication of nanomaterials and devices.

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  2. Sun CQ, Surface and nanosolid core-level shift: impact of atomic CN imperfection, PHYS REV 2004;B69:045105.
  3. Sun CQ, Li CM, Li S, Tay BK, Breaking limit of atomic distance in an impurity-free monatomic chain, PHYS REV 2004;B69:245402.
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  5. Sun CQ, Bai HL, Li S, et al., Length, strength, extensibility and thermal stability of an Au-Au bond in the gold monatomic chain, J PHYS CHEM 2004;B108:2162-7.
  6. Sun CQ, Bai HL, Tay BK, et al., Dimension, strength, and chemical and thermal stability of a single C-C bond in carbon nanotubes, J PHYS CHEM 2003;B107:7544-6.
  7. Pan LK, Sun CQ, Li CM, Elucidating information of Si-Si dimer vibration from size dependence of Raman shift, J PHYS CHEM 2004;B108:L3819-21.
  8. Sun CQ, Pan LK, Fu YQ, et al., Size dependent 2p-level shift of nanosolid silicon, J PHYS CHEM 2003; B107:L5113-5.
  9. Sun CQ, Zhong WH, Li S, et al. CN imperfection suppressed phase stability of ferromagnetic, ferroelectric, and superconductive nanosolids, J PHYS CHEM 2004;B108:1080-4.
  10. Sun CQ, Wang Y, Tay BK, et al, Correlation between the melting point of a nanosolid and the cohesive energy of a surface atom, J PHYS CHEM 2002;B106:10701-5.