可再生能源在近年來已成為科學研究的重點。在我們的日常生活中，行走、跑步或點擊滑鼠等活動經常會產生機械能，這些能量可以在日常生活中持續產生。開發具有壓電效應並能在腐蝕環境中保持穩定的材料，用來收集這些機械能並轉換為電能，是一種常被研究的方法。
氧化鋅（ZnO）是一種典型的壓電材料，具有半導體性質，經常應用於壓電奈米發電機中。然而，由於其壓電係數較低，加上其具備酸鹼兩性，與其他壓電材料相比，效率較低且容易受環境影響。為了增強其壓電係數並提高其穩定性，將ZnO核材料外覆一層更穩定的材料作為殼層，是達到這兩個目的的解決方案之一。
在本研究中，通過一系列步驟製備了ZnO/AlN核殼奈米棒結構。研究確認了該結構中ZnO核的直徑為400納米，外殼AlN的厚度為30納米，完全包裹住整個ZnO核。壓電力顯微鏡（Piezoresponse Force Microscopy，PFM）對壓電係數d33的測量進一步表明，這種結構的壓電係數相較於單獨的ZnO奈米棒或ZnO薄膜來說，達到了最高值。
此外，本研究還探討了在不使用ZnO種子層的情況下，通過水熱法在金屬薄膜（Au）上增強垂直對齊生長ZnO奈米棒的效果。該金屬薄膜既可作為底部電極，又在水熱法生長ZnO奈米棒時不需要使用ZnO種子層。此外，由於Au層不具有壓電效應，本研究能夠展示純粹來自ZnO/AlN核殼結構的壓電係數d33 。

Renewable energy sources have become a significant focus in scientific research in recent years. In our daily lives, mechanical energy is frequently generated through activities like walking, running, or clicking a mouse. This energy can be continuously produced in everyday life. Developing a piezoelectric effect possessing material and sustainable in a corrosive environment to collect this mechanical energy and convert it into electrical energy is a method commonly studied.
Zinc oxide (ZnO) is a typical piezoelectric material with semiconductor properties, frequently used in piezoelectric nanogenerators. However, due to its relatively low piezoelectric coefficient, and owning both the base and acid property it is less effective compared to other piezoelectric materials and it is easily affected by the surrounding environment. To enhance its piezoelectric coefficient and also make it more sustainable, core ZnO cover with a more stable material as a shell is one of the solutions to reach both purposes.
In this study, ZnO/AlN core/shell nanorods structure were fabricated through sequential steps. The structure of a core ZnO nanorod with a diameter of 400 nm and a shell AlN of 30 nm thickness completely wrapped the entire core is confirmed. Piezoresponse Force Microscopy d33 measurements further reveal that this structure has the highest piezoelectric coefficient compared to ZnO nanorods alone, ZnO thin film.
Moreover, in this study, enhancing the vertical alignment of hydrothermally grown ZnO nanorods on metal films (Au) without employing the ZnO seed layer is investigated. This metal film can serve as a bottom electrode and at the same time, no ZnO seed layer is needed when growing ZnO nanorods by hydrothermal method. Furthermore, because the Au layer doesn’t exhibit the piezoelectric effect, this study can show the piezoelectric coefficient d33 of the ZnO/AlN core/shell structure only.

1. Xu, Q., J. Wen, and Y. Qin, Development and outlook of high output piezoelectric nanogenerators. Nano Energy, 2021. 86: p. 106080.
2. Sripadmanabhan Indira, S., et al., Nanogenerators as a sustainable power source: state of art, applications, and challenges. Nanomaterials, 2019. 9(5): p. 773.
3. Askari, H., et al., Piezoelectric and triboelectric nanogenerators: Trends and impacts. Nano Today, 2018. 22: p. 10-13.
4. Laurenti, M., et al., Evaluation of the piezoelectric properties and voltage generation of flexible zinc oxide thin films. Nanotechnology, 2015. 26(21): p. 215704.
5. Yin, B., et al., Piezo-phototronic effect enhanced pressure sensor based on ZnO/NiO core/shell nanorods array. Nano Energy, 2016. 21: p. 106-114.
6. Wang, Z.L., Zinc oxide nanostructures: growth, properties and applications. Journal of physics: condensed matter, 2004. 16(25): p. R829.
7. Ma, T., et al., Density-controlled hydrothermal growth of well-aligned ZnO nanorod arrays. Nanotechnology, 2007. 18(3): p. 035605.
8. Chen, C.-Y., et al., ZnO/Al2O3 core–shell nanorod arrays: growth, structural characterization, and luminescent properties. Nanotechnology, 2009. 20(18): p. 185605.
9. Pinto, R.M., et al., CMOS-integrated aluminum nitride MEMS: A review. Journal of Microelectromechanical Systems, 2022. 31(4): p. 500-523.
10. Ballerini, G., K. Ogle, and M.-G. Barthés-Labrousse, The acid–base properties of the surface of native zinc oxide layers: An XPS study of adsorption of 1, 2-diaminoethane. Applied surface science, 2007. 253(16): p. 6860-6867.
11. Tichý, J., et al., Principles of piezoelectricity. Fundamentals of Piezoelectric Sensorics: Mechanical, Dielectric, and Thermodynamical Properties of Piezoelectric Materials, 2010: p. 1-14.
12. Kalinin, S.V., B. Mirman, and E. Karapetian, Relationship between direct and converse piezoelectric effect in a nanoscale electromechanical contact. Physical Review B—Condensed Matter and Materials Physics, 2007. 76(21): p. 212102.
13. Mishra, S., et al., Advances in piezoelectric polymer composites for energy harvesting applications: a systematic review. Macromolecular Materials and Engineering, 2019. 304(1): p. 1800463.
14. Jeon, B., D. Han, and G. Yoon, Piezoelectric characteristics of PVA/DL-alanine polycrystals in d33 mode. Iscience, 2023. 26(1).
15. Priya, S., et al., A review on piezoelectric energy harvesting: materials, methods, and circuits. Energy harvesting and Systems, 2017. 4(1): p. 3-39.
16. Chorsi, M.T., et al., Piezoelectric biomaterials for sensors and actuators. Advanced Materials, 2019. 31(1): p. 1802084.
17. Guerin, S., et al., Racemic amino acid piezoelectric transducer. Physical review letters, 2019. 122(4): p. 047701.
18. De Jong, M., et al., A database to enable discovery and design of piezoelectric materials. Scientific data, 2015. 2(1): p. 1-13.
19. Lee, E., et al., Characteristics of piezoelectric ZnO/AlN− stacked flexible nanogenerators for energy harvesting applications. Applied Physics Letters, 2015. 106(2).
20. Jbaily, A. and R.W. Yeung, Piezoelectric devices for ocean energy: a brief survey. Journal of Ocean Engineering and Marine Energy, 2015. 1: p. 101-118.
21. Lueng, C., et al., Piezoelectric coefficient of aluminum nitride and gallium nitride. Journal of applied physics, 2000. 88(9): p. 5360-5363.
22. Klingshirn, C.F., et al., Crystal structure, chemical binding, and lattice properties. Zinc Oxide: From Fundamental Properties Towards Novel Applications, 2010: p. 7-37.
23. Huang, R., et al., Progress of zinc oxide‐based nanocomposites in the textile industry. IET Collaborative Intelligent Manufacturing, 2021. 3(3): p. 281-289.
24. Fei, C., et al., AlN piezoelectric thin films for energy harvesting and acoustic devices. Nano Energy, 2018. 51: p. 146-161.
25. Chiu, K.-H., et al., Deposition and characterization of reactive magnetron sputtered aluminum nitride thin films for film bulk acoustic wave resonator. Thin Solid Films, 2007. 515(11): p. 4819-4825.
26. Wu, S., et al., High velocity shear horizontal surface acoustic wave modes of interdigital transducer/(100) AlN/(111) diamond. Applied Physics Letters, 2009. 94(9).
27. Das, A., et al., Realization of preferential (100) oriented AlN thin films on Mo coated Si substrate using reactive RF magnetron sputtering. Applied surface science, 2021. 550: p. 149308.
28. Chen, J., et al., The composition and interfacial properties of annealed AlN films deposited on 4H-SiC by atomic layer deposition. Materials Science in Semiconductor Processing, 2019. 94: p. 107-115.
29. Colombo, L., et al. Investigation of 20% scandium-doped aluminum nitride films for MEMS laterally vibrating resonators. in 2017 IEEE International Ultrasonics Symposium (IUS). 2017. IEEE.
30. Hvazdouski, D., M. Baranava, and V. Stempitsky, First-principles study of anisotropic thermal conductivity of GaN, AlN, and Al0. 5Ga0. 5N. 2022.
31. Zhang, Y., et al., Single-crystalline AlN/sapphire and composite electrode based ultra-high temperature surface acoustic wave devices. Journal of Physics D: Applied Physics, 2023. 56(16): p. 16LT01.
32. Qamar, A. and M. Rais-Zadeh, Coupled baw/saw resonators using AlN/Mo/Si and AlN/Mo/GaN layered structures. IEEE Electron Device Letters, 2019. 40(2): p. 321-324.
33. Kaushik, S., et al., Surface modification of AlN using organic molecular layer for improved deep UV photodetector performance. ACS Applied Electronic Materials, 2020. 2(3): p. 739-746.
34. You, D., et al., Single‐crystal ZnO/AlN core/shell nanowires for ultraviolet emission and dual‐color ultraviolet photodetection. Advanced Optical Materials, 2019. 7(6): p. 1801522.
35. Ding, R., et al., The 3.4 GHz BAW RF filter based on single crystal AlN resonator for 5G application. Nanomaterials, 2022. 12(17): p. 3082.
36. Zhao, W., et al., 15-ghz epitaxial aln fbars on sic substrates. IEEE Electron Device Letters, 2023. 44(6): p. 903-906.
37. Zhu, Y., et al., Near vacuum-ultraviolet aperiodic oscillation emission of AlN films. Science Bulletin, 2020. 65(10): p. 827-831.
38. Nguyen, H.P., Graphene-driving novel strain relaxation towards AlN film and DUV photoelectronic devices. Light: Science & Applications, 2022. 11(1): p. 164.
39. Akiyama, M., et al., Flexible piezoelectric pressure sensors using oriented aluminum nitride thin films prepared on polyethylene terephthalate films. Journal of applied physics, 2006. 100(11).
40. Mwema, F.M., E. Akinlabi, and O. Oladijo, A systematic review of magnetron sputtering of AlN thin films for extreme condition sensing. Materials Today: Proceedings, 2020. 26: p. 1546-1550.
41. Ruiz, E., S. Alvarez, and P. Alemany, Electronic structure and properties of AlN. Physical Review B, 1994. 49(11): p. 7115.
42. Yang, H., et al., A review of oriented wurtzite-structure aluminum nitride films. Journal of Alloys and Compounds, 2024: p. 174330.
43. Mohammed, A. and A. Abdullah. Scanning electron microscopy (SEM): A review. in Proceedings of the 2018 International Conference on Hydraulics and Pneumatics—HERVEX, Băile Govora, Romania. 2018.
44. Inkson, B.J., Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for materials characterization, in Materials characterization using nondestructive evaluation (NDE) methods. 2016, Elsevier. p. 17-43.
45. Epp, J., X-ray diffraction (XRD) techniques for materials characterization, in Materials characterization using nondestructive evaluation (NDE) methods. 2016, Elsevier. p. 81-124.
46. Neumayer, S.M., et al., Piezoresponse amplitude and phase quantified for electromechanical characterization. Journal of Applied Physics, 2020. 128(17).
47. Balke, N., et al., Electromechanical imaging and spectroscopy of ferroelectric and piezoelectric materials: state of the art and prospects for the future. Journal of the American Ceramic Society, 2009. 92(8): p. 1629-1647.
48. Harris, J., R. Youngman, and R. Teller, On the nature of the oxygen-related defect in aluminum nitride. Journal of Materials Research, 1990. 5(8): p. 1763-1773.
49. Liaw, H.M. and F.S. Hickernell, The characterization of sputtered polycrystalline aluminum nitride on silicon by surface acoustic wave measurements. IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 1995. 42(3): p. 404-409.
50. AlTowireb, S.M. and S. Goumri-Said, Core-Shell structures for the enhancement of energy harvesting in piezoelectric Nanogenerators: A review. Sustainable Energy Technologies and Assessments, 2023. 55: p. 102982.
51. Yang, Z., et al., Developing seedless growth of ZnO micro/nanowire arrays towards ZnO/FeS2/CuI PIN photodiode application. Scientific reports, 2015. 5(1): p. 11377.