Dear Gokul Krishna this is indeed a very interesting technical question. The answer to this question depends on how you look at microfibers. In some cases, researchers deliberately try to generate microfibers or nanofibers of certain materials. For this aspect of the question please have a look at the following relevant article:

Growth mechanism of single-crystal α-Al2O3 nanofibers fabricated by electrospinning techniques

Article Growth mechanism of single-crystal α-Al 2O 3 nanofibers fabr...

On the other hand, crystallographers don't like fiber-like crystals as they are normally useless for single-crystal X-ray diffraction. More detailed information about their growth mechanism can be found in the following article:

Fiber Crystal Growth from the Melt

Book Fiber Crystal Growth from the Melt

Unfortunately these two articles have not yet been posted as public full texts on RG. Perhaps you can get access to the full texts through your institution. In addition, I suggest that you search the "Publications" section of RG in order to find and access other relevant articles about this topic. For example, when you search for the term "Fiber Crystal Growth" and then click on "Publications" you will receive a long list of relevant articles which have been posted on RG, sometimes even as public full texts:

https://www.researchgate.net/search.Search.html?type=publication&query=Fiber%20Crystal%20Growth

Good luck with your research and best wishes!

Dear Gokul Krishna ,

in addition to the Dr. Frank T. Edelmann comments:

Wagner, Ellis, and Givargizov (see the references below) developed a study on the filamentous growth of silicon crystals from gas-phase precursors, applied for many different materials. They concluded that some impurities such as gold, platinum, or nickel are essential for the growth of filamentous crystals such as wires, tubes, or whiskers. This new concept of crystal growth was called the VLS (vapor-liquid-solid) mechanism (WAGNER; ELLIS, 1964).

In the VLS mechanism, crystal growth involves the gaseous, liquid, and solid phases. The growth of boron nitride nanotubes synthesized by CVD occurs through the VLS mechanism (LI et al., 2011).

In general, it takes place in 4 fundamental steps:

Firstly, by mass transport of primary species in the vapor phase to the gas-liquid interface.

In the second step, chemical reactions take place on the gas-liquid interface.

In the third step, diffusion occurs through the liquid phase, and finally, in the fourth and last step, precipitation occurs over the liquid-solid interface followed by subsequent incorporation of the material to the crystal lattice (GIVARGIZOV, 1975).

In the following references you have detailed description of the method.

WAGNER, R.; ELLIS, W. Vapor-liquid-solid mechanism of single crystal growth. Applied physics letters, American Institute of Physics, v. 4, n. 5, p. 89–90, 1964.

LI, J.; LIN, H.; CHEN, Y.; SU, Q.; HUANG, Q. The effect of iron oxide on the formation of boron nitride nanotubes. Chemical Engineering Journal, Elsevier, v. 174, n. 2-3, p. 687–692, 2011.

GIVARGIZOV, E. Fundamental aspects of VLS growth. In: Vapour Growth and Epitaxy. [S.l.]: Elsevier, 1975. p. 20–30.

Best regards,

WNM