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This paper is one of three papers exploring and confirming a novel high rate nanomanufacturing method using laser to induce and accelerate chemical synthesis and deposition of nanotubes. We have shown elsewhere that the growth rate of SnO 2 nanotubes by this method is a few orders faster than that by the state of the art electrochemical deposition method, the growth rate of the nanotubes is favorably affected by increasing the laser power under a constant number of scanning passes, and the process can grow nanotubes coalesced from ultrasmall particle size as small as 2 nm (Liu and Liu, 2013, "Laser Induced Chemical Solution Deposition of Nanomaterials: A Novel Process Demonstrated by Manufacturing SnO 2 Nanotubes," Manuf. Lett., 1(1), pp. 42-35). In the second paper, we have shown that this novel method is generic, demonstrated by synthesizing various metal oxide and sulfide nanotubes (Liu and Liu, "Laser-Induced Solution Synthesis and Deposition: A Generic Method to Make Metal Chalcogenide Nanotubes at High Rate With High Consistency," J. Nanoeng. Nanosyst. (accepted)). Since the performance and properties of nanomaterials are highly dependent on its structure, we explore here how the basic processing variables affect the growth rate and crystal size. Our initial finding is that (1) the growth rate can be increased by increasing the pH value of the solution, resulting in little change on the crystal size and (2) the crystal size of the manufactured ferrihydrite nanotube arrays can be controlled by changing laser scanning passes. We found the increase of the pH value from 1.33 to 2.16 almost tripled the growth rate of ferrihydrite nanotubes, while the crystal size remained little changed as revealed by the transmission electron microscopy studies. However, increasing the number of laser scanning passes at a given power could coarsen the ferrihydrite nanocrystals. The crystal structure of the nanotubes could be converted to haematite by dry furnace annealing. These initial findings demonstrated the capability and controllability of the novel process.

The mass and phase transitions among intermediate species are unique dynamics in nonclassical crystallization that are under investigation. In this research, we used a pulsed laser to initiate crystallization in its early stages and observed the crystal evolution through transitions and interactions among the intermediate species. The crystal evolution was induced and observed in situ simultaneously by the same electron beam in a transmission electron microscope without a liquid cell environment, thereby eliminating the complexity introduced by the additional nucleation in the precursor solution. The observed mass diffusion among species in an anti-Ostwald ripening way indicated that crystallization systems were composed of intermediate species in various phases. We found that these intermediate species were not like rigid building blocks but kept changing in size and phase and evolving in multistage transitions. Considering the observations, we propose a generic model by extending the classical nucleation theories to describe the dynamics of intermediate transitions and all possible crystal evolution pathways, discovered or not.