Coupling Effect of Magnetic Fields on Piezotronic and

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Coupling Effect of Magnetic Fields on Piezotronic and PiezoPhototronic Properties of ZnO and ZnO/CoO Core/Shell Nanowire Arrays 3

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Shuke Yan, Zhi Zheng, Satish Chandra Rai, Michael Retana, Manish Bhatt, Leszek Malkinski, and Weilie Zhou ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b01707 • Publication Date (Web): 29 Nov 2018 Downloaded from http://pubs.acs.org on November 30, 2018

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ACS Applied Nano Materials

Coupling Effect of Magnetic Fields on Piezotronic and Piezo-Phototronic Properties of ZnO and ZnO/Co3O4 Core/Shell Nanowire Arrays Shuke Yan,‡ Zhi Zheng,‡ Satish Rai, Michael Anthony Retana, Manish Bhatt, Leszek Malkinski, Weilie Zhou* Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana 70148, USA KEYWORDS: Piezotronic effect, Magnetic Field, Piezo-Magnetotronic effect, Piezo-PhotoMagnetotronic effect. Abstract

Piezoelectric-related multi-property coupling effects have recently attracted much attention for developing next generation multi-functional devices. In this paper, the multi-property coupling effects among magnetic field, piezoelectricity and photoexcitation were investigated in ZnO nanowire arrays. The response of the current flowing through the array to the applied magnetic field was decreasing with increasing magnetic field strength. However, due to piezo-magnetotronic effect, the magnetically induced current was magnified by one order of magnitude by applying an external stress. In contrast, under UV light illumination, the magnetically induced current response

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increased with an increment of magnetic field strength, as the magnetic field is favorable to the separation of photo-induced electron-hole pairs. The magnetically-induced current response was enhanced by at least two orders of magnitude due to the piezo-photo-magnetotronic effect. Furthermore, ZnO/Co3O4 core/shell heterojunction nanowire arrays was employed to improve the current responses up to 9 times and 3 times, under piezo-magnetotronic and piezo-photomagnetotronic engagements, respectively, attributed to the improved charge carrier separation and transportation at the core/shell interface. This phenomenon projects a potential for multi-functional piezo-magnetotronic and piezo-photo-magnetotronic device development.

Introduction Recently, multi-property coupling effects based on piezoelectric semiconductors have generated a profound impact on exploring innovative electronic devices, such as transistors,1–4 sensors,5–9 energy harvesting devices,10–17 etc. Piezotronic effect is a mutual coupling effect between piezoelectricity and semiconductor properties in the materials with asymmetric crystal structure, and can be used as a “gate” voltage to control the transport behavior of charge carriers16 to enhance the performance of traditional electronic devices as well as to develop self-powered systems. Based on this phenomenon, piezo-phototronics was further proposed by coupling the piezotronic effect with photoexcitation in order to enhance the performance of optoelectronic devices through modulating the generation, separation, recombination and transport of photo-induced electron-hole pairs,18,19 thereby establishing the foundations of piezo-phototronics. Comparatively, applied magnetic fields are implemented in numerous areas, such as data storage,20–22 medical diagnostics,23 electromagnetic sensing,24 etc. The various applications of magnetic fields are mainly based on electromagnetic induction, Hall Effect, magnetostriction,25 etc. Very recently,


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several studies on coupling magnetic fields to piezotronics/piezo-phototronic effects have been reported.1,24,26,27 For instance, Wang group proposed a magnetic-induced-piezopotential fieldeffect transistor on multilayered structure by coupling magnetic field with the piezotronic effect (piezo-magnetotronic effect).1 The piezopotential inside piezoelectric material was triggered by the deformation of the magnetic layer when a magnetic field was applied, which was used to modulate the carrier transport of the channel layer. A magnetically induced luminescence multilayer device was also reported by Hao group through coupling the magnetic field with the piezo-phototronic effect (piezo-photo-magnetotronic effect).28 The strain generated by the magnetic elastomer resulted in a piezopotential inside the piezoelectric phosphor composite, which was applied to control the light emission. It should be noted, however, that the magnetic field in the above mentioned magnetic-related coupling effects was applied to a magnetic layer to take advantage of its magnetostrictive properties. To our best knowledge, there is no report on piezomagnetotronic and piezo-photo-magnetotronic effects where the magnetic field is directly applied to the piezoelectric semiconductor to significantly modulate the charge carrier flow. In this work, ZnO nanowire (NW) arrays, as one of most commonly used piezoelectric materials in the emerging fields of piezotronics and piezo-phototronics,16,29,30 is chosen to investigate the coupling effects of piezoelectricity, magnetic field and photoexcitation. A magnetic field was engaged perpendicularly to the ZnO NW and electron transport properties were studied by applying compressive stress with/without UV light illumination. The magnetically induced current response decreased as the magnetic field increased, however, under UV light illumination the current response increased as the magnetic field increased. In addition, a paramagnetic (at room temperature) and non-magnetostrictive C3O4 layer was coated on the ZnO NW in order to form a ZnO/Co3O4 core/shell heterojunction to further improve the current response.


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Experimental Section Synthesis of ZnO NWs: ZnO NW arrays was first synthesized on SiO2 passivated indium tin oxide (ITO) coated glass substrate (CG801N, Delta Technologies LTD) through chemical vapor deposition in a three-zone tube furnace (GSL-1400X, MTI Corp.). In brief, the substrate was first cleaned by sonicating sequentially in acetone, isopropyl alcohol and deionized water, respectively. Second, Zn powders (99.9%, metals basis, Alfa Aesar) and the cleaned substrate were sequentially placed at the center zone and the right zone of the furnace. The center zone and the right zone were heated up to 900 °C and 550 °C at a rate of 10 °C/min, respectively, under a mixed gas of 300 sccm (standard cubic centimeters per minute) Argon flow and 40 sccm Oxygen flow. The reaction was maintained for 1 hour. The furnace was then cooled down naturally to room temperature. Synthesis of ZnO/Co3O4 core/shell heterostructure: 10 mM of cobalt (II) nitrate hexahydrate (Co(NO3)2•6H2O) (98%, reagent grade, Sigma-Aldrich) and hexamine (HMT) solution were dissolved into 40 mL of deionized water with molar concentrations and stirred for 1 hour at room temperature. The as-synthesized ZnO NW arrays was cut into two pieces. One piece of ZnO NW arrays was used as control sample, and another one was put in the nutrition solution, and the solution was heated and maintained at 95 °C for 12 hours as reported previously.31 After synthesis, the substrate was washed with deionized water and then annealed at 450 °C for 2 hours. Device fabrication and measurement process: In order to support NW arrays and avoid a possible short circuit between top and bottom electrodes, a 2 µm thick layer of PMMA was spin-coated on ZnO or ZnO/Co3O4 NW arrays. An Ag thin film with 100 nm thick was then sputtered on a polyester film as a top electrode, which has a groove density of 1000 grooves/mm (Edmund Optics). The top electrode was integrated with the ZnO or ZnO/Co3O4 NW arrays as shown in


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Figure 1. The Ag-coated top electrode and ITO bottom electrode were connected to a 2401 source meter (Keithley) through copper leads. The magnetic field was applied perpendicularly to the NWs, and the force was applied on top of the device on the platform of a motorized test stand (Mark-10, ESM301L). Results and Discussion The details on the ZnO and ZnO/Co3O4 core/shell NW arrays synthesis can be found in the Experimental Section and Figure 1a. The structural characterization of ZnO and ZnO/Co3O4 NW arrays is shown in Figure 2. It can be seen that the ZnO NWs with smooth surface are randomly grown out, as shown in the field emission scanning electron microscopy (FESEM) image (Figure 2a), and the diameter of the NWs is in the range of 150-200 nm. From the FESEM image in Figure 2b, it can be found that the average size and density of ZnO/Co3O4 NWs remain unchanged, but the surface of the nanowires becomes rough compared to the pristine ZnO NWs (inset in Figure 2 b). The transmission electron microscopy (TEM) image of a single ZnO/Co3O4 NW in Figure 2c demonstrates that the ZnO NW is fully covered by the Co3O4 shell with the thickness of ~10 nm. The corresponding [01-10] selected area electron diffraction (SAED) pattern in Figure 2d reveals ZnO core grown along c-axis and polycrystalline nature of Co3O4 shell layer. The diffraction rings of Co3O4 shell can be indexed to (111), (220), (311), (400), (511), and (440) lattice planes of the cubic structure (space group Fd3m). Energy dispersive spectroscopy (EDS) spectrum of a single ZnO/Co3O4 NW is displayed in Figure 2e, which reveals the existence of cobalt, zinc and oxygen, and the peaks of carbon and copper come from the TEM sample grid. The X-ray diffraction (XRD) spectra of the ZnO and ZnO/Co3O4 NWs were recorded in Figure 2f. The XRD spectrum of the pristine ZnO NWs exhibits a typical XRD pattern of ZnO NWs with high-purity wurtzite hexagonal phase (JCPDS CARD No. 36-1451)32 while the XRD spectrum of ZnO/Co3O4 NWs


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indicates a very similar pattern with the pristine ZnO NWs except some weak diffraction peaks at around 19.0°, 31.3°, 36.8°, 44.8° and 65.2°, which are well corresponding to the cubic phase of the Co3O4 (JCPDS card No. 073-1701), representing (111), (220), (311), (400) and (440) planes, respectively.31 This XRD result is in good agreement with the diffraction rings of Co3O4 shell in Figure 2d and confirms the formation of cobalt oxide phase. The fabrication and measurement procedure of the devices based on ZnO and ZnO/Co3O4 core/shell NW arrays is described in the Experimental Section and shown in Figure 1b-e. In brief, the as-synthesized ZnO NWs or ZnO/Co3O4 NWs were first spin-coated by a Poly (methyl methacrylate) (PMMA) layer to prevent the possible short circuit and provide additional support for NWs. The device was then integrated by mounting a silver-coated flexible top electrode with a unique zigzag morphology which offers an additional NWs-electrode contact area and better strain accommodation.9 The magnetic field was applied perpendicularly to NWs, the UV light illuminated from the bottom of the device and the force was applied on top of the device on the platform of a motorized test stand (Mark-10, ESM301L). The ZnO NW arrays was first measured under the magnetic field and the I-V curves are shown in Figure 3a. The rectifying property of the I-V curves indicates that a Schottky barrier was formed between ZnO NWs and Ag electrode. Though it is weak, it still can be observed that the peak currents (currents at 1V) of ZnO decreased from 3.0 to 2.1 µA as the magnetic field increased from 0 to 180 Gauss (G) because a part of free electrons inside ZnO NWs were forced to move toward the surface of ZnO NWs due to Lorentz Force. According to oxygen-related electron-trap filling mechanism,33 the electrons were trapped by the surface defects and adsorbed by oxygen ions in air, as illustrated in the schematic I of Figure 3d, therefore, the amount of free electrons was reduced, resulting in an increment of the resistance of ZnO NW. Besides, the electron


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accumulation at the ZnO NW surface generated a depletion region, which further increased the resistance of ZnO NWs. In order to investigate the coupling effect between piezotronic effect and magnetic field, the ZnO NW arrays was then measured with stresses from 0.5 N to 1.5 N as indicated in Figure S1a, S1b and Figure 3b. It can be found that the peak currents largely increased with an increment of the stress. Generally, potential barrier height modulation makes more significant contribution to current response than depletion layer modulation, therefore, we believe that the enhancement of the peak currents is mainly due to the strain-induced positive piezopotential inside ZnO NWs (schematic II of Figure 3d), which lowered the Schottky Barrier Height (SBH) between ZnO and Ag.18,34 The peak currents under stress were also decreased by applying a magnetic field. The magnetically induced peak current differences (∆𝐼 = 𝐼𝐵 ― 𝐼0, where 𝐼𝐵 and 𝐼0 are the peak currents with and without magnetic field, respectively) for the ZnO NWs with different magnetic field and stresses are summarized in Figure 3c. It can be clearly seen that the peak current differences are largely magnified when measured under a stress. The largest peak current difference (10.1 µA) with 1.5 N stress is 10 times larger than that (0.9 µA) with 0 N stress, which demonstrates that the piezo-magnetotronic coupling effect can enlarge the magnetically induced current response. To better demonstrate the piezo-magnetotronic coupling effect and improve the magnetically induced current response, a ZnO/Co3O4 core/shell NW arrays was also measured under the same conditions. Figure 4a illustrates the I-V curves of ZnO/Co3O4 NW arrays under magnetic field. Compared to the I-V curves of ZnO in Figure 3a, the magnetic-field-induced peak currents of ZnO/Co3O4 decreased from 9.9 to 4.8 µA as the magnetic field increased from 0 to 180 G. The absolute peak current difference (5.1 µA) was 5 times larger than that of ZnO (0.9 µA) because of the precipitation of Co3O4 and its rough surface, which created crystallographic defects at the


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ZnO/Co3O4 interface due to the lattice mismatch between the two materials and provided preferential adsorption site for oxygen molecules (schematic I of Figure 4d), compared to the smooth surface of ZnO NWs. In addition, the spin polarized free charges were generated in the paramagnetic Co3O4 due to the external magnetic field which contributed to an increase of free electrons to adsorb more oxygen in the ZnO/Co3O4 interface, and in turn resulted in further decrease of the current.35 The ZnO/Co3O4 NW arrays was then measured with stresses from 0.5 N to 1.5 N and the I-V curves are exhibited in Figure S2 and Figure 4b. Regarding the potential barrier height modulation, when the stress was applied to the core/shell NWs, the core ZnO NWs were bent and the strain-induced positive piezopotential lowered the SBHs of ZnO/Co3O4 and Co3O4/Ag as presented in schematic II of Figure 4d, which resulted in a large increment of the peak current of the ZnO/Co3O4 NW arrays. All the peak current differences of the ZnO/Co3O4 NW arrays are summarized in Figure 4c. It can be seen that the absolute peak current difference are almost 10 times larger than those of ZnO NW arrays under the same condition due to the significant increment of the peak current and the core/shell structure, which proves the core/shell heterostructure is capable of enhancement of the magnetically induced current response. In order to investigate the piezo-photo-magnetotronic effect, the ZnO NW arrays was then measured under magnetic field and UV light illumination (Figure 5a). The peak current (102 µA) under UV light illumination is ~35 times higher than the current (3 µA) without UV light illumination because a massive number of photo-induced electron-hole pairs were generated inside ZnO NWs resulting in a large photo-current.36 Besides, a part of photo-induced holes migrated to the surface of ZnO NWs and detached the adsorbed oxygen ions, which further increased the peak current as demonstrated in schematic I of Figure 5d. In contrast, when a magnetic field was applied, the peak current of the ZnO NW arrays increased from 102 to 132 µA under UV illumination. This


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opposite magnetically induced peak current change might be mainly due to the following two effects: a portion of electrons migrated to the surface of NW due to Lorentz Force which has a negative effect on the conductivity of NW. On the other hand, magnetic field is favorable to the separation of photo-induced electron-hole pairs and unfavorable to the recombination of electronhole pairs, which prolongs electron lifetime and has a positive effect on the conductivity of NW.37 This positive effect makes a larger contribution than the negative effect to the current response of the device (schematic II of Figure 5d), resulting in an increment of the peak current as the magnetic field was applied. The ZnO NW arrays was then measured under stresses of 0.5, 1, and 1.5 N and the I-V curves are displayed in Figure S3 and Figure 4b. The peak current became larger when a stress was applied because the strain-induced positive piezopotential decreased the SBH between ZnO and Ag (schematic III of Figure 5d). The peak currents under a stress also increased when a magnetic field was applied. All peak current difference results are summarized in Figure 5c. The peak current difference increased as the magnetic field and stress increased and the absolute largest peak current difference (146 µA) of the ZnO NWs is magnified at least two orders of magnitude by piezo-photo-magnetotronic effect compared to the absolute peak current difference (0.9 µA) of the ZnO NWs under magnetic field. This demonstrates that the piezo-photo-magnetotronic effect can further enhance the magnetic-induced current response. The piezo-photo-magnetotronic coupling effect was also investigated in a ZnO/Co3O4 NW arrays under the same conditions. Figure 6a shows the I-V curves of the ZnO/Co3O4 NW arrays under UV light illumination and magnetic field, which demonstrates that the peak current of ZnO/Co3O4 under UV illumination is much larger than that for ZnO without UV illumination due to the small band gap of Co3O4 (~2.3 eV) and core/shell heterojunction. Under UV light illumination, a massive amount of photo-induced electron-hole pairs were generated inside ZnO, Co3O4 and at the


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interface between ZnO and Co3O4 (schematic I of Figure 6d), resulting in a substantial increment of the current. Moreover, the band alignment in the core/shell heterostructure is beneficial to the separation of electrons and holes into different spatial regions, further increasing the number of free electrons.38–40 These synergistic effects resulted in a significant increment of the number of free electrons and the peak current. When measurements were done in the presence of a magnetic field, more electrons were affected by Lorentz Force (schematic II of Figure 6d), resulting in a larger magnetic-induced peak current difference in comparison to ZnO. In addition, it is expected that partially magnetized paramagnetic Co3O4 is capable of enhancing the magnetic field acting on the ZnO wires. When it was measured under stresses of 0.5, 1, and 1.5 N, the I-V curves are shown in Figure S4 and Figure 6b. It has also been observed that the peak current increased significantly when a stress was applied since the strain-induced positive piezopotential lowered the SBHs of ZnO/Co3O4 and Co3O4/Ag (schematic III of Figure 6c), which resulted in additional electrons movement to the surface of NWs, and therefore gave rise to larger peak current differences. Figure 6c summarizes all the peak current differences of the ZnO/Co3O4 NW arrays, which demonstrates that the peak current difference increased as the stress and magnetic field strength increased. The largest peak current difference (471 µA) of the ZnO/Co3O4 NW arrays is 3 times larger than that of the ZnO NW arrays under the same condition. Conclusion In summary, ZnO and ZnO/Co3O4 core/shell NW arrays have been used to explore the piezomagnetotronic and piezo-photo-magnetotronic coupling effects. As magnetic field was applied, the current response decreased, and the peak current difference was magnified by at least one order


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of magnitude through employing a stress due to piezo-magnetotronic effect. Under UV light illumination, the current response increased as the magnetic field increased because magnetic field was favorable to the separation of photo-induced electron-hole pairs. The largest magnetically induced peak current differences are enhanced by two orders of magnitude due to piezo-photomagnetotronic effect compared to the current difference without light illumination and stress. In addition, a further improvement of the magnetically induced current responses based on ZnO/Co3O4 core/shell heterojunction was achieved because the core/shell structure is favorable to the separation of photo-induced electron-hole pairs resulting in a large increment of the peak current. The mechanism of interaction of applied magnetic field with our nanostructure is markedly different than in previously reported piezo-magneto-phototronic devices based on magnetostrictive properties of the magnetic layer. The results in this work demonstrate potential applications of multi-functional devices based on piezo-magnetotronic and piezo-photomagnetotronic effects. ASSOCIATED CONTENT Supporting Information. Detailed I-V characteristic of ZnO NWs and ZnO/Co3O4 NWs devices. AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] Author Contributions ‡Shuke Yan and Zhi Zheng contributed equally to this work.


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Acknowledgements This research at AMRI, UNO was supported by the DARPA Grant No.HR0011-07-1-0032 and research grants from Louisiana Board of Regents Contract No. LEQSF (2011-13)-RD-B-08 and LEQSF (2016-17)-ENH-TR-34. References (1)

Liu, Y.; Guo, J.; Yu, A.; Zhang, Y.; Kou, J.; Zhang, K.; Wen, R.; Zhang, Y.; Zhai, J.; Wang, Z. L. Magnetic-Induced-Piezopotential Gated MoS2 Field-Effect Transistor at Room Temperature. Adv. Mater. 2018, 30 (8), 1704524.

(2)

Han, W.; Zhou, Y.; Zhang, Y.; Chen, C.; Lin, L.; Wang, X.; Wang, S.; Wang, Z. L. StrainGated Piezotronic Transistors Based on Vertical Zinc Oxide Nanowires. ACS Nano 2012, 6 (5), 3760–3766.

(3)

Wang, L.; Liu, S.; Feng, X.; Xu, Q.; Bai, S.; Zhu, L.; Chen, L.; Qin, Y.; Wang, Z. L. Ultrasensitive Vertical Piezotronic Transistor Based on ZnO Twin Nanoplatelet. ACS Nano 2017, 11 (5), 4859–4865.

(4)

Kwon, S.; Hong, W.; Jo, G.; Maeng, J.; Kim, T.; Song, S.; Lee, T. Piezoelectric Effect on the Electronic Transport Characteristics of ZnO Nanowire Field-Effect Transistors on Bent Flexible Substrates. Adv. Mater. 2008, 20 (23), 4557–4562.

(5)

Fu, Y.; Nie, Y.; Zhao, Y.; Wang, P.; Xing, L.; Zhang, Y.; Xue, X. Detecting Liquefied Petroleum Gas (LPG) at Room Temperature Using ZnSnO3/ZnO Nanowire PiezoNanogenerator as Self-Powered Gas Sensor. ACS Appl. Mater. Interfaces 2015, 7 (19), 10482–10490.

(6)

Xue, F.; Zhang, L.; Tang, W.; Zhang, C.; Du, W.; Wang, Z. L. Piezotronic Effect on ZnO Nanowire Film Based Temperature Sensor. ACS Appl. Mater. Interfaces 2014, 6 (8), 5955–


12

Page 13 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


5961. (7)

Yu, R.; Pan, C.; Chen, J.; Zhu, G.; Wang, Z. L. Enhanced Performance of a ZnO NanowireBased Self-Powered Glucose Sensor by Piezotronic Effect. Adv. Funct. Mater. 2013, 23 (47), 5868–5874.

(8)

Zhou, Y. S.; Hinchet, R.; Yang, Y.; Ardila, G.; Songmuang, R.; Zhang, F.; Zhang, Y.; Han, W.; Pradel, K.; Montès, L.; et al. Nano-Newton Transverse Force Sensor Using a Vertical GaN Nanowire Based on the Piezotronic Effect. Adv. Mater. 2013, 25 (6), 883–888.

(9)

Yan, S.; Rai, S. C.; Zheng, Z.; Alqarni, F.; Bhatt, M.; Retana, M. A.; Zhou, W. Piezophototronic Effect Enhanced UV/Visible Photodetector Based on ZnO/ZnSe Heterostructure Core/Shell Nanowire Array and Its Self-Powered Performance. Adv. Electron. Mater. 2016, 2 (12), 1600242.

(10)

Yang, Y.; Guo, W.; Zhang, Y.; Ding, Y.; Wang, X.; Wang, Z. L. Piezotronic Effect on the Output Voltage of P3HT/ZnO Micro/Nanowire Heterojunction Solar Cells. Nano Lett. 2011, 11 (11), 4812–4817.

(11)

Hu, G.; Guo, W.; Yang, X.; Zhou, R.; Pan, C.; Wang, Z. L. Enhanced Performances of Flexible ZnO/Perovskite Solar Cells by Piezo-Phototronics Effect. Nano Energy 2016, 23, 27–33.

(12)

Zhang, Y.; Yang, Y.; Wang, Z. L. Piezo-Phototronics Effect on Nano/Microwire Solar Cells. Energy Environ. Sci. 2012, 5 (5), 6850.

(13)

Zhou, Y. S.; Wang, K.; Han, W.; Rai, S. C.; Zhang, Y.; Ding, Y.; Pan, C.; Zhang, F.; Zhou, W.; Wang, Z. L. Vertically Aligned CdSe Nanowire Arrays for Energy Harvesting and Piezotronic Devices. ACS Nano 2012, 6 (7), 6478–6482.

(14)

Park, K.; Xu, S.; Liu, Y.; Hwang, G.; Kang, S. L.; Wang, Z. L.; Lee, K. J. Piezoelectric


13


Page 14 of 23

BaTiO3 Thin Film Nanogenerator on Plastic Substrates. Nano Lett. 2010, 10 (12), 4939– 4943. (15)

Mao, Y.; Zhao, P.; McConohy, G.; Yang, H.; Tong, Y.; Wang, X. Sponge-Like Piezoelectric Polymer Films for Scalable and Integratable Nanogenerators and SelfPowered Electronic Systems. Adv. Energy Mater. 2014, 4 (7), 1301624.

(16)

Wang, Z. L.; Wu, W. Piezotronics and Piezo-Phototronics: Fundamentals and Applications. Natl. Sci. Rev. 2014, 1 (1), 62–90.

(17)

Gupta, M. K.; Kim, S.-W.; Kumar, B. Flexible High-Performance Lead-Free Na0.47K0.47Li0.06NbO3 Microcube-Structure-Based Piezoelectric Energy Harvester. ACS Appl. Mater. Interfaces 2016, 8 (3), 1766–1773.

(18)

Wang, Z. L. Piezopotential Gated Nanowire Devices: Piezotronics and Piezo-Phototronics. Nano Today 2010, 5 (6), 540–552.

(19)

Zhang, Y.; Jie, W.; Chen, P.; Liu, W.; Hao, J. Ferroelectric and Piezoelectric Effects on the Optical Process in Advanced Materials and Devices. Adv. Mater. 2018, 30 (34), 1707007.

(20)

Singh, S. C.; Singh, D. P.; Singh, J.; Dubey, P. K.; Tiwari, R. S.; Srivastava, O. N. Metal Oxide Nanostructures; Synthesis, Characterizations and Applications. Plasma Sci. Technol. 2008.

(21)

Wu, W.; Changzhong Jiang, C. J.; Roy, V. A. L. Recent Progress in Magnetic Iron Oxide– semiconductor Composite Nanomaterials as Promising Photocatalysts. Nanoscale 2015, 7 (1), 38–58.

(22)

Hu, Y.; Qian, H.; Mei, T.; Guo, J.; White, T. Facile Synthesis of Magnetic Metal (Mn, Co, Fe, and Ni) Oxide Nanosheets. Mater. Lett. 2010, 64 (9), 1095–1098.

(23)

Reiss, G.; Hütten, A. Applications beyond Data Storage. Nat. Mater. 2005, 4 (10), 725–726.


14

Page 15 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(24)

Cui, N.; Wu, W.; Zhao, Y.; Bai, S.; Meng, L.; Qin, Y.; Wang, Z. L. Magnetic Force Driven Nanogenerators as a Noncontact Energy Harvester and Sensor. Nano Lett. 2012, 12 (7), 3701–3705.

(25)

Zaidi, N. S.; Sohaili, J.; Muda, K.; Sillanpää, M. Magnetic Field Application and Its Potential in Water and Wastewater Treatment Systems. Sep. Purif. Rev. 2014, 43 (3), 206– 240.

(26)

Peng, M.; Zhang, Y.; Liu, Y.; Song, M.; Zhai, J.; Wang, Z. L. Magnetic-MechanicalElectrical-Optical Coupling Effects in GaN-Based LED/Rare-Earth Terfenol-D Structures. Adv. Mater. 2014, 26 (39), 6767–6772.

(27)

Wong, M.-C.; Chen, L.; Tsang, M.-K.; Zhang, Y.; Hao, J. Magnetic-Induced Luminescence from Flexible Composite Laminates by Coupling Magnetic Field to Piezophotonic Effect. Adv. Mater. 2015, 27 (30), 4488–4495.

(28)

Huang, L.; Bai, G.; Wong, M.; Yang, Z.; Xu, W.; Hao, J. Magnetic-Assisted Noncontact Triboelectric Nanogenerator Converting Mechanical Energy into Electricity and Light Emissions. Adv. Mater. 2016, 28 (14), 2744–2751.

(29)

Wang, Z. L. From Nanogenerators to Piezotronics—A Decade-Long Study of ZnO Nanostructures. MRS Bull. 2012, 37 (09), 814–827.

(30)

Zhang, Y.; Ram, M. K.; Stefanakos, E. K.; Goswami, D. Y. Synthesis, Characterization, and Applications of ZnO Nanowires. J. Nanomater. 2012, 2012, 1–22.

(31)

Mariscal, A. R.; Marquez, M. C. Evolution of Cobalt Oxide Nanostructures on Glass Substrate via Two Step Solution Route Synthesis. IOP Conf. Ser. Mater. Sci. Eng. 2017, 205, 012028.

(32)

Lupan, O.; Emelchenko, G. A.; Ursaki, V. V; Chai, G.; Redkin, A. N.; Gruzintsev, A. N.;


15


Page 16 of 23

Tiginyanu, I. M.; Chow, L.; Ono, L. K.; Cuenya, B. R.; et al. Synthesis and Characterization of ZnO Nanowires for Nanosensor Applications. Mater. Res. Bull. 2010, 45 (8), 1026–1032. (33)

Wang, Y.; Ramos, I.; Santiago-Avilés, J. J. Optical Bandgap and Photoconductance of Electrospun Tin Oxide Nanofibers. J. Appl. Phys. 2007, 102 (9), 093517.

(34)

Miller, D. R.; Akbar, S. A.; Morris, P. A. Nanoscale Metal Oxide-Based Heterojunctions for Gas Sensing: A Review. Sensors Actuators B Chem. 2014, 204, 250–272.

(35)

Deka Boruah, B.; Misra, A. Effect of Magnetic Field on Photoresponse of Cobalt Integrated Zinc Oxide Nanorods. ACS Appl. Mater. Interfaces 2016, 8 (7), 4771–4780.

(36)

Pan, Z.; Peng, W.; Li, F.; He, Y. Piezo-Phototronic Effect on Performance Enhancement of Anisotype and Isotype Heterojunction Photodiodes. Adv. Funct. Mater. 2018, 28 (29), 1706897.

(37)

Lu, M.-L.; Weng, T.-M.; Chen, J.-Y.; Chen, Y.-F. Ultrahigh-Gain Single SnO2 Nanowire Photodetectors Made with Ferromagnetic Nickel Electrodes. NPG Asia Mater. 2012, 4 (9), e26.

(38)

Chen, M.; Zhao, B.; Hu, G.; Fang, X.; Wang, H.; Wang, L.; Luo, J.; Han, X.; Wang, X.; Pan, C.; et al. Piezo-Phototronic Effect Modulated Deep UV Photodetector Based on ZnOGa2O3 Heterojuction Microwire. Adv. Funct. Mater. 2018, 28 (14), 1706379.

(39)

Ouyang, W.; Teng, F.; Fang, X. High Performance BiOCl Nanosheets/TiO2 Nanotube Arrays Heterojunction UV Photodetector: The Influences of Self-Induced Inner Electric Fields in the BiOCl Nanosheets. Adv. Funct. Mater. 2018, 28 (16), 1707178.

(40)

Yang, W.; Hu, K.; Teng, F.; Weng, J.; Zhang, Y.; Fang, X. High-Performance SiliconCompatible Large-Area UV-to-Visible Broadband Photodetector Based on Integrated Lattice-Matched Type II Se/n-Si Heterojunctions. Nano Lett. 2018, 18 (8), 4697–4703.


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Figure 1. Schematic illustration of (a) the synthesis process, and (b-e) the device fabrication/measurement process. (b) As-synthesized ZnO or ZnO/Co3O4 NWs on ITO glass substrate, (c) a ~2 μm PMMA layer was spin-coated onto the NWs, (d) the device was integrated with Ag-coated top electrode and (e) the device was located on homemade stage where load was applied on top of the device, UV light was illuminated from the bottom of the device and magnetic field was parallel to the electrodes.


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Figure 2. FESEM images of (a) pristine ZnO NWs and (b) ZnO/Co3O4 core/shell NWs, insets in a and b are the high-resolution images. The scale bars in the insets are 100 nm. (c) TEM image of a single ZnO/Co3O4 core/shell NW with corresponding (d) [01-10] SAED pattern and (e) EDS spectrum. (f) XRD pattern of pristine ZnO NWs and ZnO/Co3O4 core/shell NWs.


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Figure 3. I-V characteristics of ZnO NWs device under (a) 0 N and (b) 1.5 N stress. (c) The summary of the peak current difference of the device under various stress. (d) Schematics of energy bands alignment and electron movement under magnetic field directed perpendicularly out of the paper.


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Figure 4. I-V characteristics of ZnO/Co3O4 NWs device under (a) 0 N and (b) 1.5 N stress. (c) The summary of the peak current difference of the device under various stress. (d) Schematics of energy bands alignment and electron movement under magnetic field directed perpendicularly out of the paper.


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Figure 5. I-V characteristics of ZnO NWs device under UV illumination and (a) 0 N and (b) 1.5 N stress. (c) The summary of the peak current difference of the device. (d) Schematics of energy bands alignment and electron movement under magnetic field directed perpendicularly out of the paper.


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Figure 6. I-V characteristics of ZnO/Co3O4 NWs device under UV illumination and (a) 0 N and (b) 1.5 N stress. (c) The summary of the peak current difference of the device under various stress. (d) Schematics of energy bands alignment and electron movement under magnetic field directed perpendicularly out of the paper.


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Abstract Graphic


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Coupling Effect of Magnetic Fields on Piezotronic and

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