# Micro-Nano Machining TiO\({}_{2}\) Patterns without Residual Layer by Unconventional Imprinting
## 3 Results and Discussion
With the extension of contact time, there is no significant change of the topography and height of PMMA/Ti\({}^{4+}\) lines, as shown in Figure 3. This is because the mechanism of FRTI and traditional HI in the patterning process is different. FRTI is based on the fact that the interface force between the substrate and the patterned material is stronger than that between the template and the patterned material, and the high\(-\)efficiency patterning process of PMMA/Ti\({}^{4+}\) is completed for 5 s.  
Under the optimization condition of 5 s (contact time) and 4000 rpm (coating speed), the effect of PMMA/Ti\({}^{4+}\)concentration (0.5%, 1% and 1.5%) on the topography of PMMA/Ti\({}^{4+}\) lines was investigated, seeing AFM images and cross\(-\)section analysis in Figure 4. The atmosphere outside the PDMS is unsaturated with xylene vapor, leading to a pressure gradient (\(\Delta\)P) [26] from inside to outside the PDMS, resulting in the solvent gradually evaporating through the PDMS. During the evaporation, the xylene flow brings solute to the side walls of the PDMS, which is the phenomenon of \"solvent flow\" [19; 23]. As solute is less at low concentration, solute can be driven to the side wall edge of PDMS cavity under the action of solvent flow, as shown in Figure 4a. When the concentration is low (the solute is less), the solute can be all driven to the edge of the side wall of the PDMS cavity under the action of the solvent flow, resulting in the higher-resolution lines than the original template, as shown in Figure 4a. When the concentration is high (the solute is more), one part of the solute driven to the edge of the side wall of the PDMS cavity, and the other part of the solute be concentrated in the middle of the PDMS cavity, as shown in Figure 4b,c. Through the above research, the PMMA/Ti\({}^{4+}\) lines with different resolution can be fabricated by adjusting the concentration of solution, showing the superiority of this method. From the above discussion, the resolution of PMMA/Ti\({}^{4+}\) lines, fabricated under the concentration of 1.5%, the coating speed of 4000 rpm and the contact time of 5 s, is almost the same as that of the original PDMS template, defined as inducer 1. However, the resolution of PMMA/Ti\({}^{4+}\) lines, fabricated under the concentration of 0.5%, the coating speed of 4000 rpm and the contact time of 5 s, is higher than that of the original PDMS template, defined as inducer 2. Figure 5a shows the SEM image of TiO\({}_{2}\) lines (TiO\({}_{2}\) L1) without residual layer, obtained by hydrothermal assembly [27; 28; 29] for 4 h of inducer 1, which periodicity is in good agreement with that of inducer 1. Figure 5b shows the SEM image of TiO\({}_{2}\) lines without residual layer (TiO\({}_{2}\) L2), obtained by hydrothermal  
Figure 3: AFM images of PMMA/Ti\({}^{4+}\) lines obtained with different contact time: (**a**) 5 s, (**b**) 60 s and (**c**) 180 s.  
self-assembly for 4 h of inducer 2, which periodicity is in good agreement with that of inducer 2 and the resolution is much higher than TiO\({}_{2}\) L1. Figure 5c shows the SEM image of TiO\({}_{2}\) lines without residual layer (TiO\({}_{2}\) L3), obtained by hydrothermal self-assembly for 8 h of inducer 2. Due to the overgrowth of TiO\({}_{2}\) nano-rods, TiO\({}_{2}\) nano-rods on the adjacent lines are connected with each other, resulting in that the resolution of TiO\({}_{2}\) L3 is lower than TiO\({}_{2}\) L2. The minimum width of TiO\({}_{2}\) line is 200 nm in Figure 5b. Meanwhile, the phase composition of the synthesized sample is shown in the XRD diagram of Figure S1, and rutile TiO\({}_{2}\) can be observed.