研究目的
To enhance the nonlinear optical (NLO) properties of L,L-diphenylalanine (FF) nanostructures through structural modifications by fluorination, and to evaluate the effects of fluorination on the piezoelectric response and nonlinear optical properties.
研究成果
Fluorination of dipeptides that self-assemble into microstructures/nanostructures significantly enhances nonlinear optical and piezoelectric properties. The fluorinated FF dipeptide, Fl-FF, shows a piezoresponse coefficient (d15) of 600 pm/V and at least 20 times higher SHG intensity compared to FF nanotubes. This work demonstrates the potential of fluorinated self-assembled biological nanostructures in enhancing nonlinear optical and piezoresponse properties.
研究不足
The study focuses on the enhancement of NLO properties and piezoelectric response through fluorination of FF dipeptides. The exact symmetry of Fl-FF nanotubes and its impact on SHG polarimetry patterns are not fully determined and are subjects for future work.
1：Experimental Design and Method Selection:
The study involved the synthesis of fluorinated FF dipeptides (Fl-FF) and their self-assembly into nanotubes. Density-functional theoretical calculations were used to understand the minimum energy conformers of Fl-FF. The effects of fluorination on piezoelectric response and nonlinear optical properties were evaluated using piezoresponse force microscopy (PFM) and second harmonic generation (SHG) polarimetry.
2：Sample Selection and Data Sources:
FF and Fl-FF nanotubes were fabricated using the liquid vapor phase method. Individual tubes were isolated for SHG polarimetry and piezoelectric force spectroscopy.
3：List of Experimental Equipment and Materials:
A Q-switched YAG:Nd3+ laser operating at 1064 nm for SHG setup, a scanning probe microscope (Model: Park-NX10, Park Systems) for PFM, and a cooled EMCCD camera (Photometrics Evolve 512) for capturing SHG images.
4：Experimental Procedures and Operational Workflow:
The SHG setup was configured in transmission geometry with a spot size of 100 μm or in a reflection geometry using a micro-SHG imaging setup. PFM was used to characterize the surface topography and piezoresponse of the samples.
5：Data Analysis Methods:
The piezoelectric d15 coefficient was deduced from the slopes of the PFM amplitude as a function of the applied dc voltage. SHG intensity was compared between FF and Fl-FF nanotubes.
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