Investigation and optimization of polarization properties of self-assembled carbon nanotube films

Abstract

Manipulating the optical polarization states has been demonstrated to be effective for communications, signal processing, and sensing. As a unique two-dimensional material, oriented carbon nanotube (CNT) films possess a strong polarization dependence effect in ultra-wide optical spectrum and fascinating physical properties. Furthermore, its remarkable compatibility with the micro-nano fabrication process enables its great potential in the integration with microelectromechanical (MEMS) devices. However, the polarization performance of CNT film is sensitive to many factors, which makes the integration with devices challenging when precise locations and angles are required. We address this issue by assembling CNTs into a tightly packed and aligned film from which the polarization properties were explored related to film thickness, tube alignment, and internal impurity, etc. The mechanisms of how the CNT film polarization properties were determined by such factors were analyzed. Some practically effective methods to enhance its polarization capability were proposed simultaneously. More specifically, a sample possessing a degree of polarization (DOP) up to 99% and transmittance over 45% was obtained through proper regulations. The validated optimization makes the aligned CNT films more feasible and valuable for the integration of the CNT polarizers with MEMS technology.

Pixelated Micropolarizer Array Based on Carbon Nanotube Films

“…Highly aligned CNT film is prepared by capillary zippering of vertically aligned CNT forest sheets [ 22 ]. A detailed process for the preparation of CNT films can be found in our previous work [ 24 ]. A 500 μm thick quartz wafer serves as a substrate for applications in the visible spectrum.…”

“…The second tier of self-assembled CNT film is grown directly on the protective layer ( Figure 2 h). The catalyst lines [ 24 ] of the second CNT film have a 45-degree angular offset from those of the first tier of CNT film. After the self-assembly process of the CNT film, the orientation of the second layer of the CNT film has a 45-degree angular offset from those in the first layer;…”

“…However, for polarization imaging, a DOP of more than 0.9 provides polarimetric signal preservation of approximately 90%, which is within consideration [ 29 ]. The polarization capacities of the CNT film is mainly relying on the stability of the grown environment, which reaches 0.99 of DOP in our previous work at 632 nm wavelength [ 24 ]. The DOP differences between the two tiers are generated by the uncertainties in the different growth batches.…”

“…The remarkable compatibility of self-assembled CNT films and semiconductor processes was reported by Hayamizu Y. et al [ 22 ] and Fan S. et al [ 23 ], which demonstrated the scalable fabrication of CNT devices. Our previous study [ 24 ] demonstrated that for capillary force-assembled CNT films, the optimum thickness of the film is approximately 0.7~0.8 μm (density 0.59 g/cm 3 ) corresponding to the incident light of 632 nm wavelength. With optimized growth conditions and a purification process, the film achieved a transmittance of 45% and a DOP of 99%.…”