Vapor-liquid-solid growth mechanism

For their rich potential in various applications described in the previous section, the synthesis and assembly of various ZnO micro and nanostructures have been extensively explored using both gas-phase and solution-based approaches. The most commonly used gas-phase growth approaches for synthesizing ZnO structures at the nanometer and micrometer scale include physical vapor deposition (40, 41), pulsed laser deposition (42), chemical vapor deposition (43), metal-organic chemical vapor deposition (44), vapor-liquid-solid epitaxial mechanisms (24, 28, 29, 45), and epitaxial electrodeposition (46). In solution-based synthesis approaches, growth methods such as hydrothermal decomposition processes (47, 48) and homogeneous precipitation of ZnO in aqueous solutions (49-51) were pursued. 

Remarkable is the presence of drop-shaped structures at the tips of cylinder-like fragments (Fig. 1, b-c). Similar structures are inherent in well-known vapor-liquid-solid (VLS) mechanism of crystal growth. If this is the case, the copper particles entering the compression flow due to a weak erosion of the MFC copper electrodes... 

An Au-catalysed chemical vapour transport and condensation (CVTC) process was used to produce ZnO nanorods and nanowires on Si02 and Si substrates [58], ZnO nanorods with a wide band gap (3.37eV) are regarded as promising candidates for the fabrication of nanoelectronic devices. In this work, EDX spectra of the tip and the body of ZnO nanorods were captured which indicates that Au-Zn alloyed droplets were present at the tips of the fabricated nanorods pointing to a nanorod growth via a vapor-liquid-solid (VLS) mechanism. 

Hejazi SR, Hosseini HR, Sasani Ghamsari M. The role of reactants and droplet interfaces on nucleation and growth of ZnO nanorods synthesized by vapor—liquid—solid (VLS) mechanism. J Alloys Compd 2008 455 353-7. 

The most important nanomaterial synthesis methods include nanolithography techniques, template-directed syntheses, vapor-phase methods, vapor-liquid-solid (VLS) methods, solution-liquid-solid (SLS) approaches, sol-gel processes, micelle, vapor deposition, solvothermal methods, and pyrolysis methods [1, 2]. For many of these procedures, the control of size and shape, the flexibility in the materials that can be synthesized, and the potential for scaling up, are the main limitations. In general, the understanding of the growth mechanism of any as-... 

R. S. Wagner and W. C. Ellis, Vapor-liquid-solid mechanism of single crystal growth, Appl. Phys. Lett., 4,1964, 89-90... 

In all of these processes it is possible to increase the yield of whiskers by adding metallic impurities, and the sublimation process requires such additions. The vapor—liquid—solid (VLS) growth mechanism is often thought to be involved. 

Carter, J.F. VFS (vapor-liquid-solid) newly discovered growth mechanism on the lunar surface . Science 1973, 181, 841-842. 

Nanowhiskers are very promising products of nanothechnology with broad applications in near future [1]. Nevertheless, there are several unsolved scientific problems related to formation and growth of nanowhiskers. The aim of our paper is to give more insight to these problems. The influence of substrate parameters and gas flow are under discussion. The scheme of nanowhisker growth developed in the frame of vapor-liquid-solid mechanism (VLS), is shown in Fig. 1. 

Wagner, R.S. and Ellis, W.C. (1964) Vapor-liquid-solid mechanism of single crystal growth, Appl. Phys. Lett. 4, 89 (1965) Vapor-liquid-solid mechanism of crystal growth and its application to silicon, Trans. Met. Soc. AIME 233, 1053. The description of the VLS mechanism. Now used for more than Si. 

A film is deposited in a conventional chemical vapor deposition (CVD) process when the gaseous reactants are presented with a large hot support surface. Supported growth of whiskers occurs also when the gaseous reactants are presented with discrete hot metal catalyst particles located on the surface of a suitable substrate. Unsupported whisker growth occurs when hot metal catalyst particles are freely interspersed with the gaseous reactants in the vapor phase. The most common mechanism for whisker growth is a vapor-liquid-solid transformation, and the most versatile VLS process is a metal particle catalyzed chemical vapor deposition. 

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