Effects of Humidity on the Microstructure and the Ferroelectric Properties of Sol-Gel grown P(VDF-TrFE) Films

Young Joon Ko,진다운,Dae Sol Kong,Jong Hoon Jung 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.4

We report the microstructure and the ferroelectric properties of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] films grown under various humidity conditions and synthesis times by using a sol-gel method. When the synthesis time under a humid condition was short (approximately 30 min), the moisture in the environment affected only the surface morphology without any loss of ferroelectricity for the P(VDF-TrFE) films. In contrast, when the synthesis time was long (approximately 90 min), the moisture strongly affected the microstructure and the ferroelectric properties of P(VDF-TrFE). The transparent P(VDF-TrFE) film became opaque at high humidity. Scanning electron microscopy revealed numerous pores on the surface of and inside the film. The pores reduced the Young's modulus considerably from 4.15 to 0.97 GPa for the films grown at 20 and 80% relative humidity, respectively. In addition, the ferroelectric hysteresis loop disappeared at humidities above 60%. This work provides upper limits for the humidity and the synthesis time for the growth of high-quality P(VDF-TrFE) films by using a sol-gel method.

Lead-free (K,Na)NbO3 Thick Films for Flexible Non-volatile Memory Applications

Kwak Yeong Min,Lee Tae Kwon,Kong Dae Sol,Ko Young Joon,Jeong Dong Geun,Jung Jong Hoon 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.9

We report the sol-gel fabrication and electrical characterization of flexible (K,Na)NbO3 (KNN) thick films. Muscovite mica allows the growth of high-quality polycrystalline KNN thick films with flexible functionality. Because of the trade-off between increase of grain-size and volatilization of alkaline ions, the electrical polarization is optimized at certain temperature of 720 °C. The remnant and saturation polarization of flexible KNN films were recorded to Pr=10.3 μC/cm2 and Ps = 23.3 μC/cm2, respectively, which are quite close to those of rigid films with the same chemical compositions. The KNN thick films are bendable even up to bending radius of R = 3.1 mm, and the Pr and Ps at bending states are almost the same as compared to those at unbending state. Even in the convex and concave bending, the KNN thick films show excellent non-volatile memory characteristics. The Pr is almost the same even after the 108 times of switching and the 104 sec of retention.

Proton-irradiated Pb(Zr_0.52Ti_0.48)O₃ thick films for flexible non-volatile memory applications

Lee, Tae Kwon,Kong, Dae Sol,Jin, Da Woon,Yun, Shinhee,Yang, Chan-Ho,Jung, Jong Hoon ELSEVIER 2019 Current Applied Physics Vol.19 No.6

<P><B>Abstract</B></P> <P>We investigated the ferroelectricity in proton-irradiated flexible Pb(Zr<SUB>0.52</SUB>Ti<SUB>0.48</SUB>)O<SUB>3</SUB> (PZT) thick films and their non-volatile memory characteristics. The Ni-Cr metal foil substrate allowed high-quality polycrystalline PZT films with flexible functionality to be fabricated using conventional sol-gel and high-temperature annealing methods. The 10-MeV proton-irradiated PZT film exhibited an almost square polarization−electric field hysteresis curve with saturated (<I>P</I> <SUB>s</SUB>) and remnant (<I>P</I> <SUB> <I>r</I> </SUB>) polarizations of 18.9 and 17.0 μC/cm<SUP>2</SUP>, respectively; which are slightly lower than as-grown PZT with <I>P</I> <SUB>s</SUB> = 28.7 μC/cm<SUP>2</SUP> and <I>P</I> <SUB> <I>r</I> </SUB> = 24.3 μC/cm<SUP>2</SUP>. The <I>P</I> <SUB> <I>r</I> </SUB> did not decrease even after 1000 cycles of continuous bending and unbending at a bending radius of 2.14 mm and decreased slightly to ∼80% of its initial value after 10<SUP>5</SUP> s. Although the <I>P</I> <SUB> <I>r</I> </SUB> decreased to ∼55% after 10<SUP>10</SUP> cycles, the electric polarization remained switchable under positive and negative electric fields. These characteristics suggest that the flexible PZT films could be utilized in non-volatile memory device applications in environments with high doses of proton irradiation, such as those in aeronautics and nuclear power plants.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Sol-gel growth of flexible PZT thick films on a Ni-Cr metal foil substrate. </LI> <LI> Large saturated and remnant electric polarization in proton-irradiated films. </LI> <LI> Mechanical stability, long retention time, and high fatigue resistance even after the high energy proton-irradiation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Floating buoy-based triboelectric nanogenerator for an effective vibrational energy harvesting from irregular and random water waves in wild sea

Kim, Dong Yeong,Kim, Hyun Soo,Kong, Dae Sol,Choi, Moonkang,Kim, Hak Bum,Lee, Jae-Hyoung,Murillo, Gonzalo,Lee, Minbaek,Kim, Sang Sub,Jung, Jong Hoon Elsevier 2018 Nano energy Vol.45 No.-

<P><B>Abstract</B></P> <P>Water waves in wild sea have unique characteristics of being huge, random, irregular, and of low frequency. To effectively harvest such vibrational energy, any devices should be light enough to float, sensitive even to small amplitudes, durable against harsh environmental conditions, easily replaceable after long-term use, and easily linked to form a network. Here, a floating buoy-based triboelectric nanogenerator (FB-TENG) is demonstrated to effectively harvest the vibrational energy with full satisfaction of these requirements. The FB-TENG consisted simply of a power generation unit, which was packed in an acrylic case, and a height-adjustable support, which was attached to a floating buoy. Even for the small amplitude of water waves, the height-adjustable support provides vigorous vibration at the power generation unit; which was sufficient to power 30 light-emitting diodes (LEDs), and operate a digital thermo-hygrometer and an anenometer. Under saltwater (salinity of 40%), thermal shocks (temperature range of 4–60°C), and strong ultraviolet irradiation (power of 10 W), the FB-TENG generates stable electric power by virtue of the acrylic packing of the power generation units. The FB-TENG also generates electric power from the various and mixed amplitudes and frequencies of water waves coming from all directions. Furthermore, the FB-TENG can easily be integrated into a network for high-power generation. This work provides a significant step forward in the harvesting of the blue energy of water waves, and the realization of self-powered sea mark and weather monitoring systems in wild sea.</P> <P><B>Highlights</B></P> <P> <UL> <LI> High power generation for small amplitude of water waves coming from all directions. </LI> <LI> Simple and safe Ar-plasma etching for the enhanced triboelectrification of PTFE. </LI> <LI> Strong resistance against harsh environmental conditions of wild sea. </LI> <LI> Self-powering of light emitting diodes, thermo-hygrometer, and anemometer. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Microwave-welded single-walled carbon nanotubes as suitable electrodes for triboelectric energy harvesting from biomaterials and bioproducts

Kim, Hyun Soo,Kim, Dong Yeong,Kwak, Ji Hye,Kim, Jong Hun,Choi, Moonkang,Hyung Kim, Do,Lee, Dong Woo,Kong, Dae Sol,Park, Jinhong,Jung, Sunshin,Lee, Gwan-Hyoung,Lee, Minbaek,Jung, Jong Hoon Elsevier 2019 Nano energy Vol.56 No.-

<P><B>Abstract</B></P> <P>Biomaterials and bioproducts have unique characteristics of being renewable, abundant, biodegradable, and having rough surfaces. In order to implement them into highly efficient triboelectric nanogenerator (TENG) applications, the contact electrode should be cheap, flexible, able to withstand outdoor environments, and have a rough surface. Here, microwave-welded single-walled carbon nanotubes (SWCNTs) are shown to effectively harvest the mechanical vibrational energy from biomaterials and bioproducts. Selective and flash microwave heating provides firm welding of SWCNTs to a polycarbonate substrate without significant losses in flexibility, transparency, and electrical conductivity. Microwave-welded SWCNT electrodes were successfully deployed as single-electrode TENGs to harvest energy from cellulose film, hanji paper, and cherry leaf. The cellulose- and paper-based TENGs showed the quite stable triboelectric outputs even after excessive contacts and a long period of time. The leaf-based TENG showed the significantly modified triboelectric outputs due to the moisture evaporation induced shrinkage and roughness of the surface. The SWCNT electrode generated ca. ten- and two-fold larger voltage and current, respectively, than those obtained using an indium-tin oxide (ITO) electrode. Using a fan-shaped leaf-based TENG, multiple light emitting diodes and a cellular phone were successfully powered without a battery. This work implies that the microwave-welded SWCNT electrode with rough pored surface and strong resistance against environmental shocks could be a good candidate for the outdoor biomaterials and indoor bioproducts implemented TENGs to harness random- and low-frequency vibrational energy.</P> <P><B>Highlights</B></P> <P> <UL> <LI> 1 Microwave welding of single-walled carbon nanotubes on a flexible substrate. </LI> <LI> 2 Rough and pored surface of SWCNT for increased contact area with cellulose, paper, and leaf. </LI> <LI> 3 Moisture evaporation dependent triboelectric outputs in leaf-based triboelectric nanogenerator. </LI> <LI> Powering multiple light emitting diodes and charging a cellular phone. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>