Plasmon‐Assisted Nanopoling of Poly(Vinyl Difluoride) Films

Abstract

without post-treatment. [15,16] Common strategies of generating β-phased PVDF include mechanical (stretching, pressing, and shearing) poling, [17][18][19] electric poling, [20] electrospinning, [21][22][23] and other unconventional methods. [24][25][26] These methods always require harsh conditions (high temperature and high voltage) and complicated instruments. In some cases, where the PVDF films are thin (<300 nm), poling can be achieved simply by thermal annealing; [27] however, it has no local selectivity, which is not compatible for integrated piezoelectronic nanodevices.Optical field due to its electromagnetic feature can also be applied for poling molecules. [28][29][30] It has unique advantages of local selectivity, fast modulation, and remote controllability. However, such poling is only transient, which is not useful for bistate devices that require long-term stability.Plasmons, collective oscillations of the free electron gas density at optical frequency, can be a good electromagnetic field condenser as well as an absorber of light. It converts photon energy efficiently into huge amount of local heating, which has been widely used for nanowelding, particle deformation, seawater desalination, and photothermal therapy. [31][32][33][34][35][36][37] By using small gold nanoparticles (Au NPs) as the heating source, it can be potentially used as a nanoheater to selectively pole the PDVF films with light, which is beyond the diffraction limit.In this paper, we show that the thermal effect induced by plasmonic heating can pole the PVDF films. As the plasmonic heating of individual Au NP is in the scale of <10 nm, it provides a facile and efficient strategy for nanophase transformation, which has important applications in piezoelectric nanodevices and high-density data storage. [38,39] Results and DiscussionThe thermal effect can improve the chain movement, which promotes the phase transformation of PVDF. [9,10] As shown in Figure 1a, the PVDF films annealed at 90 °C present a Raman peak at 840 cm −1 (β phase), while the unannealed films show a peak at 797 cm −1 (α phase), which matches the Raman spectrum of the PVDF powders (Figure S1, Supporting Information). This thermal poling is very reproducible to PVDF films of different thicknesses as all of them exhibit the β phase peak after annealing although the intensities are different (Figure 1b). The intensity of α phase peak increases as the PVDF films get thicker, which is because Plasmonic nanoheating can be utilized to induce nanophase transformation, which has important implications for nano-optoelectronics, nanopiezoelectronics, and high-density data storage. Herein, optical poling of poly(vinyl difluoride) (PVDF) is shown with the assistance of surface plasmons. The ultrathin PVDF films are sandwiched between gold nanoparticles (Au NPs) and a gold film. By irradiating the Au NPs with continuouswave laser, nanoannealing of the PVDF films is realized, which locally transforms the PVDF from α phase to β phase as evidenced by Raman spectroscopy. This nanopha...

Plasmon-assisted nanophase engineering of titanium dioxide for improved performances in single-particle based sensing and photocatalysis

“…Plasmonic nanoheating induced by the confined thermal effect has been applied to nanolithography, [43][44][45][46] nanojetting, 47 nanoparticle deformation, [48][49][50] nanophase transitions 51,52 and nanoprinting. 53,54 Here, instead of using global annealing, we locally anneal the TiO 2 films with the assistance of surface plasmons, which generates much smaller domains of phase change compared to UV laser annealing.…”

Enhanced plasmonic sensing of single gold nanoparticles with narrowed resonance linewidths

“…Plasmonic structure based spectroscopy has been a powerful sensing technique to monitor chemicals and their reactions, 1,2 morphological evolution, 3,4 phase transitions 5 and biomedical processes. 6 Its broad applications are attributed to localized surface plasmon resonance (LSPR) with enhanced light–matter interactions at the deep subwavelength scale.…”

Digital Selective Reversible Phase Control of Monolithically Integrated Heterogeneous Piezoelectric Polymer for Frequency Dependent Unimorph

“…[5,21] Overcoming the conventional single-phase producing processes, researchers tried to pattern the ferroelectric property in a single PVDF layer. [22][23][24][25][26][27] Spatially controlled crystalline phases with different polarization (e.g., α-, βand γ-phase) could produce strengthened or programmed reactivity to external stimuli [22,26] that can be applied to a high density of arrayed electronic devices such as sensors or memory devices. Furthermore, it also can achieve evolved and programmed responses to external stimuli through the difference in reactivity of each phase in a single PVDF which is not allowed in conventional single-phase producing processes.…”

“…[24,25] Extreme laser condition to randomize the polarization was so slow that a long processing time was required and film destruction was observed. Recently, studies using plasmonic nanoparticles to increase laser absorption and changes in the phases of PVDF have been reported, [26,27] however, the level of phase transition was poor. Moreover, no studies on the laser-driven phase transition mechanism on a molecular scale were investigated.…”