characteristic gives polyvinylidene fluoride (PVDF) an advantage over its higher cost (≈10× more expensive) copolymer relative, P(VDF-TrFE). [5] Conversely, given the high coercive field intrinsic to PVDF, fabrication of ultrathin films is essential to achieving low voltage operation of this polymer. [6] These thin films must be dense, smooth, and contain the correct ferroelectric crystalline phases. [7] However, unlike the copolymer P(VDF-TrFE), the processing of PVDF to produce these thin films is problematic. Stringent processing conditions are necessary to transform the paraelectric α phase of PVDF to the desirable ferroelectric β, γ, or δ polymorphs.Several reports have demonstrated robust ferroelectric devices based on semicrystalline PVDF in the ferroelectric phases, induced either via mechanical stretching, [8][9][10] electroforming, [11][12][13][14][15] controlled thermal annealing, [16][17][18][19][20] or by applying additives. [21][22][23] Stress-induced αto β-phase transition in PVDF films by mechanical stretching is applicable only to thick films, rendering it an impractical route for thin films that can operate at low voltages. Likewise, additives such as clays, carbon nanotubes, graphene, or polymers like polymethylmethacrylate are known to promote β-phase crystallization; these additives, however, limit the minimum achievable thickness and increase surface roughness of such films due to limited solubility with PVDF. To counter these problems, controlled annealing of PVDF thin films from melts using multistep heating and cooling can increase the content of the crystalline ferroelectric phases. [21] These processing conditions are time consuming and require annealing temperatures as high as 180 °C. More recently, studies by de Leeuw et al. successfully demonstrated that ultrathin PVDF films (down to 10 nm) in the α phase transforms to the δ polymorph when poled in high electric fields, resulting in the observation of ferroelectric behavior. These films were cast by spinning or doctor blading PVDF from solution under controlled humidity and/or at elevated substrate temperatures. [14,15] Here, we demonstrate a technique that uses a very short exposure to light (less than a millisecond), resulting in the transformation of the α-phase of PVDF to the ferroelectric β-phase, as depicted in Figure 1. Compared to the rates and modes of energy transfer found in conventional ovens and rapid photothermal processing, this technique can result in energy transfer in hundreds of microseconds. [24] At such time Thin films of polyvinylidene fluoride (PVDF) enable access to efficient hybrid devices that operate at low voltages. However, the preparation of thin films from solution typically yields nonferroelectric crystalline phases that require additional processing steps to transform the nonferroelectric phases to the more desirable ferroelectric polymorphs. Here, a rapid photonic annealing technique is reported that induces an αto β-phase transformation in PVDF thin films, opening up the opportunity to process the m...
