Stress and piezoelectric properties of aluminum nitride thin films deposited onto metal electrodes by pulsed direct current reactive sputtering

A new non-destructive evaluation technique to detect cracks emanating from the inner surface (inner cracks) of a high-pressure hydrogen storage cylinder was developed by means of mechanoluminescence (ML) sensor consisting of SrAl 2 O 4 :EuML material and epoxy resin. To visualize the inner crack,a sheet ML sensor was attached onto the outer surface of the storage cylinder subjected to hydraulic pressure cycling with the maximum pressure of 45 MPa. The ML pattern was changed with an increase in the cycle number and the ML sensor could visualize the inner crack. The stress analysis by the finite element method clarified that the ML sensor provided unique equivalent strain distribution associated with stress concentration at the crack tip, i.e. the distance between two points having high equivalent strains was inversely proportional to the crack depth;consequently, the growth behavior of the inner crack was non-destructively quantified with the ML sensor attached on the outer surface.

structures attracted world-wide attention in order to ensure effective maintenance and avoid recurrence of such severe disasters. [1][2][3] In December 2017, a serious incident happened at a Shinkansen bullet train of Japan due to anomalous load caused fatigue cracks and rupture in an undercarriage, [4] and this sudden incident further enhanced the urgent necessity to predict the fracture (damage) of infrastructures. Since conventional magnetic particle testing (MT), penetrant testing (PT), and ultrasonic testing (UT) methods are difficult for precise largescale infrastructure diagnosis, many techniques were proposed on this topic in recent years, such as sensing techniques of electrical resistance or capacitive MEMS strain sensors and piezoelectric sensors were proposed for precise strain or anomaly detection, but these methods still had limitations for strain imaging on real world structures due to the sensor scale and/or spatial resolution. [5][6][7][8] On the other hand, new types of sensors based on photoelectric methods such as assembled nanowires/nanotubes or microstructured rubber layers, [9][10][11][12][13][14][15] stretchable and flexible strain sensor with conductive nanostructure for sensitive detection of human motion, [16] piezotronic/piezo-phototronic-effect enhanced light emitting smart sensors, [17,18] and flexible or bionic mechanosensors were proposed as effective sensing techniques for dynamic imaging of pressure or stress and diagnosing movement disorders in high-resolution. [19][20][21][22][23] However, fabrication methods of the abovementioned nanowire array or flexible smart sensors are complicated, and they are inconvenient for scalable precise stress/strain imaging and especially difficult for large-scale application and onsite real world infrastructures.Herein, we report another mechanism of largely scalable and flexible strain sensor using elasticoluminescent smart paint for challenge to solve worldwide structural diagnosis problems ranging from micro to macroscales. The elasticoluminescence presented in this study also called elastico-mechanoluminescence is a unique form of mechanoluminescence (ML) that can generate repeatable and reproducible light emission during elastic deformation. [24][25][26][27][28][29] The new scalable elasticoluminescent strain sensor has great significance on high sensitivity and precise dynamic stress/strain imaging, and onsite fracture inspection and diagnoses on large-scale infrastructures. The innovative scalable strain sensor would prospectively open a Precise dynamic stress/strain imaging is critical for a broad range of research and engineering analyses ranging from micrometer to meter-scales, but there is no precise multiscale strain sensor, especially for onsite real-time structural health monitoring. Here, a scalable elasticoluminescent strain sensor is presented for solving worldwide structural diagnosis problems ranging from micrometer to meter-scales. Significant progress has recently been made on both highly sensitive elasticoluminescent sensor...

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Ultrasensitive and sustainable near‐infrared (NIR)‐emitting piezoluminescence is observed from noncentrosymmetric and ferroelectric‐phase Sr3Sn2O7 doped with rare earth Nd3+ ions. Sr3Sn2O7:Nd3+ (SSN) with polar A21am structure is demonstrated to emit piezoluminescence of wavelength of 800–1500 nm at microstrain levels, which is enhanced by the ferroelectrically polarized charges in the multipiezo material. These discoveries provide new research opportunities to study luminescence properties of multipiezo and piezo‐photonic materials, and to explore their potential as novel ultrasensitive probes for deep‐imaging of stress distributions in diverse materials and structures including artificial bone and other implanted structures (in vivo, in situ, etc).

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Abstractc‐Axis oriented aluminum nitride (AlN) thin films are successfully prepared on amorphous polyimide films by radiofrequency magnetron reactive sputtering at room temperature. Structural analysis shows that the AlN films have a wurtzite structure and consist of c‐axis oriented columnar grains about 100 nm wide. The full width at half maximum of the X‐ray diffraction rocking curves and piezoelectric coefficient d33 of the AlN films are 8.3° and 0.56 pC N–1, respectively. The AlN films exhibit a piezoelectric response over a wide temperature range, from –196 to 300 °C, and can measure pressure within a wide range, from pulse waves of hundreds of pascals to 40 MPa. Moreover, the sensitivity of the AlN films increases with the number of times it was folded, suggesting that we can control the sensitivity of the AlN films by changing the geometric form. These results were achieved by a combination of preparing the oriented AlN thin films on polyimide films, and sandwiching the AlN and polymer films between top and bottom electrodes, such as Pt/AlN/polyimide/Pt. They are thin (less than 10 μm), self powered, adaptable to complex contours, and available in a variety of configurations. Although AlN is a piezoelectric ceramic, the AlN films are flexible and excellent in mechanical shock resistance.