Amorphous Nanomaterials. Lin Guo
of a specific system, multiple growth mechanisms can occur simultaneously. It depends on the values of global parameters such as supersaturation, local factors that include interface curvature, and materials parameters such as phase stability versus particle size. The growth process may include the traditional direct connection of atoms, the connection of crystal clusters, the connection of amorphous particles and the subsequent crystallization or maturation, and the oriented or non-oriented connection of crystal particles and recrystallization. Ostwald ripening can occur in all particles to provide free radicals for the main particles. At the same time, twins, stacking faults, and dislocations can result from the attachment of crystalline particles. It can be found that the predictive understanding of the theory of particle-connected crystallization is helpful for the further development of amorphous nanomaterial design and synthesis.
1.5 Summary and Outlook
Although many studies have confirmed the significance of amorphous nanomaterials, their development is still in their infancy. For example, it is widely believed that amorphous materials have SRO, but their atomic arrangement cannot be accurately defined, even with the help of AC-TEM. Intense debates regarding whether they could exhibit medium-range ordering at the nanometer scale or even LRO are still ongoing. In addition, compared with the highly ordered arrangement of atoms in crystals, the atomic disorder of amorphous materials endows them highly unsaturated centers on the surface. If the unsaturated centers were all active sites, the catalytic performance would be improved by an order of magnitude. However, the reported research has not achieved such an improvement. Therefore, as an emerging discipline, the study of amorphous nanomaterials is of great significance.
At the same time, the synthesis of amorphous nanomaterials is only in the exploration stage. Most of the as-reported synthesis method is incomprehensive and non-systematic, while systematical and universal methods are needed. Limited by the isotropic feature of amorphous structure, the morphology of naturally growing amorphous materials are spherical particles. If 1D materials are expected, an external force must be applied to confine the growth direction, for example, electrospinning and chemical vapor deposition. The preparation of 3D materials with regular morphology can only rely on the hard template method and then etching the template to obtain a polyhedron frame or shell. The template-free self-growth of amorphous materials with specific and programmed morphology is extremely difficult. Thus, researches on the design and synthesis of amorphous nanomaterial should be comprehensively reviewed to summarize the laws. In addition, the study of the relationship between structure and related properties of the amorphous nanomaterials and their potential applications will greatly promote the development of amorphous nanomaterials.
References
1 1 Hilden, L.R. and Morris, K.R. (2004). Physics of amorphous solids. J. Pharm. Sci. 93: 3–12.
2 2 Anderson, P.W. (1995). Through the glass lightly. Science 267: 1615–1616.
3 3 Couzin, J. (2005). What is the nature of the glassy state. Science 309: 83–83.
4 4 Zhang, D.-F., Zhang, H., Guo, L. et al. (2009). Delicate control of crystallographic facet-oriented Cu2O nanocrystals and the correlated adsorption ability. J. Mater. Chem. 19: 5220–5225.
5 5 Fisher, I.R., Kramer, M.J., Islam, Z. et al. (2000). Growth of large single-grain quasicrystals from high-temperature metallic solutions. Mater. Sci. Eng. A 294: 10–16.
6 6 Zhang, Z., Ye, H.Q., and Kuo, K.H. (1985). A new icosahedral phase with m35 symmetry. Philos. Mag. A 52: L49–L52.
7 7 Yue, Y., Zheng, K., Zhang, L., and Guo, L. (2015). Origin of high elastic strain in amorphous silica nanowires. Sci. China Mater. 58: 274–280.
8 8 Hirata, A., Guan, P., Fujita, T. et al. (2011). Direct observation of local atomic order in a metallic glass. Nat. Mater. 10: 28–33.
9 9 Steno, N. (1669). De solido intra solidum naturaliter contento Dissertationis Prodromus. Florence: sub signo Stellae.
10 10 Bragg, W.L. (1913). The structure of some crystals as indicated by their diffraction of X-rays. Proc. R. Soc. London Ser. A 89: 248–277.
11 11 Liebig, B. (1840). On amorphous quinine: as it exists in the substance known in commerce as quinoidine. Prov. Med. Surg. J. 10: 265.
12 12 Gore, G. (1862). On the properties of electro-deposited antimony. Proc. R. Soc. Lond. 12: 323–331.
13 13 Buckel, W. and Hilsch, R. (1954). Einfluß der Kondensation bei tiefen Temperaturen auf den elektrischen Widerstand und die Supraleitung für verschiedene Metalle. Zeitschrift für Physik 138(2): 109–120.
14 14 Turnbull, D. (1950). The supercooling of aggregates of small metal particles. JOM 2: 1144–1148.
15 15 Klement, W., Willens, R., and Duwez, P. (1960). Non-crystalline structure in solidified gold–silicon alloys. Nature 187: 869–870.
16 16 Zhang, T., Inoue, A., and Masumoto, T. (1991). Amorphous Zr–Al–TM (TM=Co, Ni, Cu) alloys with significant supercooled liquid region of over 100 K. Mater. Trans., JIM 32: 1005–1010.
17 17 Wang, J., Li, R., Hua, N., and Zhang, T. (2011). Co-based ternary bulk metallic glasses with ultrahigh strength and plasticity. J. Mater. Res. 26: 2072–2079.
18 18 Liu, Y.H., Wang, G., Wang, R.J. et al. (2007). Super plastic bulk metallic glasses at room temperature. Science 315: 1385–1393.
19 19 Hofmann, D.C., Suh, J.Y., Wiest, A. et al. (2008). Designing metallic glass matrix composites with high toughness and tensile ductility. Nature 451: 1085–1094.
20 20 Constable, F.H. (1925). The catalytic action of copper. Part VII. A study of the effect of pressure on the rate of dehydrogenation of alcohols. Proc. R. Soc. Lond. 107: 279–286.
21 21 Smith, G.V., Brower, W.E., Matyjaszczyk, M.S., and Pettit, T.L. (1981). Metallic glasses: new catalyst systems. Stud. Surf. Sci. Catal. 7: 355–363.
22 22 Brower, W., Matyjaszczyk, M., Pettit, T., and Smith, G. (1983). Metallic glasses as novel catalysts. Nature 301: 497–499.
23 23 Wang, J.Q., Liu, Y.H., Chen, M.W. et al. (2012). Rapid degradation of azo dye by Fe-based metallic glass powder. Adv. Funct. Mater. 22: 2567–2570.
24 24 LaMer, V.K. and Dinegar, R.H. (1950). Theory, production and mechanism of formation of monodispersed hydrosols. J. Am. Chem. Soc. 72: 4847–4854.
25 25 Peng, X., Wickham, J., and Alivisatos, A.P. (1998). Kinetics of II-VI and III-V colloidal semiconductor nanocrystal growth: “focusing” of size distributions. J. Am. Chem. Soc. 120: 5343–5344.
26 26 Oxtoby, D.W. (1998). Nucleation of first-order phase transitions. Acc. Chem. Res. 31: 91–97.
27 27 Weiner, S., Sagi, I., and Addadi, L. (2005). Choosing the crystallization path less traveled. Science 309: 1027–1028.
28 28 Gower, L.B. (2008). Biomimetic model systems for investigating the amorphous precursor pathway and its role in biomineralization. Chem. Rev. 108: 4551–4627.
29 29 Gebauer, D. and Colfen, H. (2011). Prenucleation clusters and non-classical nucleation. Nano Today 6: 564–584.
30 30 De Yoreo, J.J., Gilbert, P.U., Sommerdijk, N.A. et al. (2015). Crystallization by particle attachment in synthetic, biogenic, and geologic environments. Science 349: 498.
2 Local Structure and Electronic State of Amorphous Nanomaterials
2.1 Spherical Aberration-Corrected Transmission Electron Microscopy
2.1.1 Introduction
With the recent developments in hardware attachments to achieve both probe- and image-corrected microscope geometries so as to obtain a sub-Angstrom resolution, the spherical aberration-corrected transmission electron microscopy (Cs-TEM) is nowadays recognized as a powerful tool for study condensed matter physics and materials science. These advantages are meeting the growing demand of nanosciences and nanotechnology