Discovery of robust yet reversibly switchable electric dipoles at reduced dimensions is critical in advancing nanoelectronics devices. Energy bands flat in momentum space generate robust localized states that are activated independently of each other. We determined flat bands exist and induce robust yet independently switchable dipoles exhibiting a unique ferroelectricity in HfO2. Flat polar phonon bands in HfO2 cause extreme localization of electric dipoles within its irreducible half-unit-cell-widths (~3 Å). Contrary to conventional ferroelectrics with spread dipoles, those intrinsically localized dipoles are stable against extrinsic effects such as domain walls, surface exposure, and even down-to-angstrom-scale miniaturization. Moreover, the sub-nm-scale dipoles are individually switchable without creating any domain-wall energy cost. This offers unexpected opportunities for ultimately-dense unit-cell-by-unit-cell ferroelectric switching devices directly integrable into silicon technology.

Internet of things (IoT), has triggered considerable interest in triboelectric nanogenerators (TENGs) as renewable and sustainable power sources, [1][2][3][4] owing to their high output power, [5,6] cost-effectiveness, [7] and high energy conversion efficiency. [8][9][10] The wide-availability and high functionality of TENGs offers itself to several practical applications. [11][12][13][14] Crucial to the successful implementation of TENGs in practical applications is to generate sufficient output power, usually stored in a capacitor or a battery, to operate the devices. [15][16][17][18] Strategies to enhance the output performance of TENGs are generally based on increasing of the transferred charge density between two contacted surfaces, as the electric potential is critically dependent on it. [19][20][21][22] Although the principle of contact-electrification has long been studied, [23][24][25] but whose mechanisms are still unclear. Recently, surface-states and electron cloud/potential models have been employed to explain the contact electrification mechanism. However, these models are limited to metal-semiconductors and metal-insulators, i.e., they may be not currently compatible with metal-polymers. [26,27] Other strategies have relied on the choice of materials in the triboelectric series with electronic and structural modifications, [28] such as a large work-function difference, [29,30] high porosity, [31,32] large dielectric constant, [33][34][35] and large surface roughness. [36][37][38] The maximum charge density of these TENGs in practical environments, however, requires additional processes, such as charges injection and poling process under high electric field. [35,[39][40][41] In particular, the injection process was quite efficient in increasing the charge density because it was considered to be limited by air breakdown. [38] Actually, the dielectric strengths of the polymers are larger than that of the air. The charge density was reached to 260 and 283 µC m −2 in TENGs with single-layered film and multilayered film, respectively. [40,41] Recently, several modifications to amplify the current flowing through the external circuit have been successfully demonstrated. [6,20,42] Metal-dielectric-metal structures or metal-metal contacts have been introduced, proven to increase the charge density of the TENG by several times.Since TENGs are driven by vibrations in the environment and human kinetics, the frequencies of the mechanical forces High-output triboelectric nanogenerators (TENGs) are demonstrated based on polyimide (PI)-based polymers by introducing functionalities (e.g., electronwithdrawing and electron-donating groups) into the backbone. The TENG based on 6FDA-APS PI, possessing the most negative electrostatic potential and the low-lying lowest unoccupied molecular orbital level, produces the highest effective charge density of about 860 µC m −2 in practical working conditions with the ion injection process. This may be ascribed to the excellent charge-retention characteristics as well as the enh...

A sustainable highly charged C60-functionalized polyimide is introduced as the dielectric of a TENG, which generates higher output power and a superior charge density with slower charge decay rate, compared with a perfluoroalkoxy alkane film-based TENG.

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