Direct femtosecond laser writing of nanochannels by carbon allotrope transformation

Abstract

Existing approaches for creating durable nanochannels are complex, expensive, and time-consuming. Here, a novel approach is presented in which a femtosecond laser is used to directly write optically accessible nanochannels with arbitrary lengths. Their cross-sections resemble slits and have dimensions that differ by two orders of magnitude. These nanochannels form between an ultra-thin nanocrystalline diamond film and a glass substrate, and their cross-sectional dimensions can be tuned via laser pulse energy. Microscopic investigations show that the laser writing process converts a portion of the sample into a nanostrip, and dedicated experiments indicate that this originates from laser light absorption in the NCD film. The nanostrip is flanked by two nanochannels formed through the delamination of the film. Within the nanostrip, there is non-diamond carbon that plays a vital role in supporting the delaminated portions of the film. This non-diamond carbon is produced when diamond changes into a different carbon allotrope. Besides investigating the mechanism underlying nanostrip formation in depth, film patterning through laser writing is also presented. To demonstrate the applicability of the laser-written nanochannels, a nanofluidic device is fabricated. The nanochannels of the device fill with water via capillary action, as supported by reflectance measurements and simulations. By bypassing complex fabrication techniques and utilizing a durable material system, this work opens doors to manufacturing affordable devices reliant on durable nanochannels, thereby offering promising prospects for future applications.