S

O

pen Access

Frontiers in Nanotechnology

Front Nanotechnol Volume 1(1): 20191

ReseaRch aRticle

Investigation of nanogenerators composed of zinc oxide nanostructures prepared by thermal oxidation of metal zincAlex Axelevitch*, I. Lapsker

Department of Microelectronics and Nanotechnology, Holon Institute of Technology (HIT), 52 Golomb St., Holon 5810201, Israel

AbstractWe used the glass, sit all and polyimide substrates. Grown nanostructures were applied to fabricate the nanogenerators using the piezoelectric effect. It was found that the more developed nanostructures grow on inhomogeneities of the gold-zinc interfaces. Internal resistance of fabricated nanogenerators significantly influences on the produced electrical signal. Generated voltage of grown nanogenerators was from 0.4 V up to 1.3 V depending on the voltage applied to the exciting transducers. Structure and electrical properties of grown systems were studied. This paper shows the possibility to use zinc oxide nanostructures as nanogenerators as the acoustic signal sensors.

Keywords: Piezoelectric nanogenerator; Zinc oxide; nano-structures; acoustic sensor.

IntroductionOur life is based on production and utilization of energy. We burn down a fossil fuel to heat and light up our homes, prepare food, and for quick travels. One of the main problems in the energy production field is the limitation of usual fossil fuel sources. At the same time, traditional energy production technologies significantly influence on the global climate and the ecological state of our environment. This is the very important reason to find novel renewable and ecologically pure alternative energy sources. One of such sources is the utilization of the piezoelectric effect for energy generation. Various piezoelectric materials are widely investigated in recent years. Zinc oxide (ZnO) is one of those materials. Thin films of ZnO have attracted great attention due to their unique piezoelectric and piezooptic properties, making them suitable for various microelectronics and optoelectronics applications, such as surface acoustic wave devices, optical fibers, transparent conductive electrodes for solar cells and optoelectronic material for blue and ultraviolet (UV) lasers [1]. ZnO nanostructured thin layers are widely applied also for the preparation the cold cathodes due to their enhanced field emission properties [2-4].

Recently, an interest to nanostructured ZnO systems has increased. Zinc oxide nanostructures appear as nanoparticles [5, 6], nano-rings [7], nano-rods [8], nano-wires and nano-belts [9]. Zinc oxide nanostructures may be obtained by various methods: air annealing of ZnO films [8], electrochemical deposition [10], vapor-liquid-solid (VLS) growth process [11], spray pyrolysis growth [12], hydrothermal method [13], sol-gel method [14], magnetron sputtering [15-17].

Due to their piezoelectric properties, ZnO nanostructures may

be used for energy generation and harvesting. In other words, these nanostructures enable to convert mechanical energy into useful electricity. Piezoelectric materials, such as barium titanate (BaTiO3), lead titanate (PbTiO3), lead zirconium titanate (PZT; PbZrxTi1-xO3) or zinc oxide (ZnO), allow the conversion of mechanical energy, in forms of oscillation, vibration, contact pressure or bending, into electricity [18-19]. The piezoelectric effect is a significant property of non-centrosymmetric crystals and it is in the displacement of the positive and negative centers of charge under tensile or compressive forces. Nanogenerators are based on this principle and enable simple constructions for the mechanical energy converting into electricity [20-21]. So, the nanogenerators can find very large spectrum of application such as they may be applied to all flexible and dynamic surfaces like cloth or shoes, motor roads and car wheels etc.

ZnO nanostructures may be also grown through thermal oxidation of metallic zinc (Zn) films [22-25]. This method is simple and cost effective. Main goal of mentioned above works was growth and characterization of nanowires from ZnO. In these works, the influence of the oxidation time and annealing temperature on the structural, electrical and optical properties was studied. However, piezoelectric properties have not been considered in these works.

In our work, we investigated possibility to build nanogenerators composed of ZnO nanostructures grown by thermal oxidation

Correspondence to: Alex Axelevitch, Department of Science, Holon Institute of Technology (HIT), 52 Golomb St., Holon 5810201, Tel no: +972-3-5026844, Israel, Email: alex_a[AT]hit[DOT]ac[DOT]il

Received: Aug 16, 2018; Accepted: Aug 20, 2018; Published: Sept 04, 2018

Axelevitch A (2018) Investigation of nanogenerators composed of zinc oxide nanostructures prepared by thermal oxidation of metal zinc

Front Nanotechnol Volume 1(1): 20192

of the vacuum evaporated Zn films on the rigid and flexible substrates. The Zn films were thermally oxidized at temperature of 550-6500C for rigid substrates and 3000C for flexible polymer substrates. The purpose of the present study is to build nanogenerators composed of various ZnO nanostructures and examine their nanogenerator performance.

Experimental details

(Figure 1) presents a schematic cross-sectional view of the experimental samples. The thin film system consists of a rigid or flexible substrate, adhesion enhancing thin chromium (Cr) layer, gold (Au) sublayer, ZnO nanostructured thin film, silicon monoxide (SiO) protecting layer and upper aluminum (Al) electrode. Here, the Au sublayer plays a role of the ZnO growth promoter. The Au layer was deposited through the specific masks with round and strip shapes. Cr and Au thin films were deposited using home-made triode sputtering setup enabling growth of dense polycrystalline metal layers at low pressure of ~1 mTorr and with the sputtering voltage of 1.5 kV [26]. Deposition duration was of 1 min for the Au layer and 10 min for the Cr sublayer. Thin films of Al and SiO were deposited by vacuum evaporation method from tungsten evaporators and tantalum closed boxes respectively at residual pressure. ZnO thin films were prepared by the various ways: thermal evaporation of metal Zn on the various substrates with following thermal treatment, magnetron sputtering of ZnO target at argon pressure of 160 mTorr during 60 min using the sputtering voltage of 1.5 kV on the substrate heated up to 1500C and triode sputtering of ZnO target at low pressure conditions of 1 mTorr with the same sputtering voltage and deposition duration on the substrate heated up to 1800C in the triode sputtering system [27].

Thin ZnO based structures were grown on glass, sitall and polyimide substrates. Table 1 represents the substrate types, mask patterns for Au and Zn films and annealing conditions for the preparation of the ZnO layer from metal Zn coatings. To prepare the multilayer systems according the Fig. 1, we

implemented series of operations which are shown in the flow chart, (Figure 2) Firstly, after substrates preparation and cleaning, the Cr sublayer was grown. After that the gold layer was deposited through suitable mask, and then the Zn layer was grown according to the condition given in Table 1. After Zn deposition, the samples were annealed and after that, they were coated by protecting SiO layers and upper aluminum electrodes. Connecting wires were glued to the Au and Al surfaces using the conductive silver paint G3790 of “BELGAR”.

The transmittance spectra of the grown ZnO thin films in the wavelength range of 200-1100 nm were recorded using UNICO UV-2800 UV/VIS spectrometer. Resistivity of the grown films was studied using standard four-point method. The surface structure of the deposited films was studied using the computerized metallurgical microscope “Nicon-Optiphot 100” with optical magnification of up to ×1600 and a Leica Stereoscan 430 scanning electron microscope (SEM), operating in 20 keV. Composition of the films was estimated using an energy dispersive spectrometer (EDS), mounted on a Stereoscan-430.

To evaluate piezoelectric properties of grown nanostructures, we used the sound generator Agilent 33120A, the multimeter MM570A and oscilloscope Agilent DS07012A. To provide a periodic mechanical impact on the studied samples, the BaTiO3 piezoelectric transducers of Murata were applied. (Figure 3-a) illustrates the application of the standard transducer. Evaluated device was put on the surface of the transducer which was connected with the sound generator. Output voltage produced by the device was studied using oscilloscope. If the applied frequency is in the acoustic range, the transducer produces the acoustic oscillations. (Figure 3-b) represents the principal electrical measurement scheme. This measurement circuit allows us to monitor the studied signals, as well as rectify the obtained voltage and measure it. To estimate the value of generated power, the rectifying scheme on the Schottky diodes was build.

Device Number Substrate Au layer Zn layer Thermal treatmentEnvironment Temperature Time

#1 Glass Rounded islands Continuous film Air 5500C 5h#2 Sitall Strips Continuous film Air 6000C 5h#3 Glass Rounded islands Rounded islands Air 6500C 5h#4 Polyimide Continuous film Rounded islands Air 3000C 2h

Table 1: Types of the substrates and annealing conditions.

Figure 1: A cross-sectional view of the grown thin film system

Axelevitch A (2018) Investigation of nanogenerators composed of zinc oxide nanostructures prepared by thermal oxidation of metal zinc

Front Nanotechnol Volume 1(1): 20193

Figure 2: Flow chart of operations to fabricate the piezoelectric devices.

Figure 3: A) Application of the standard transducer to exciting mechanical vibrations in the studied device. (B) The principal electrical measurement scheme (b).

A

B

Axelevitch A (2018) Investigation of nanogenerators composed of zinc oxide nanostructures prepared by thermal oxidation of metal zinc

Front Nanotechnol Volume 1(1): 20194

Results and discussions(Figure 4) presents transmittance spectra recorded for a pure glass substrate and glasses coated by ZnO film, deposited using the magnetron sputtering method and by the triode sputtering method. As can be seen, these films are transparent in the visible range. The resistivity values of these films are in the range of (1.8-2)×10-2 Ω⋅cm. The film deposited by triode sputtering looks denser than films grown by magnetron sputtering with higher refraction index due to the higher energy of sputtered

particles at the triode process. Comparison of the measured transmittance spectra with the measurements provided other researchers [12, 28], approves that our films consist of ZnO, however our films are of low thickness, approximately 150-200 nm. Optical bandgap of deposited ZnO films was calculated used the well-known Tauc’s method. This value was 3.27 eV for the films preparated by the magnetron sputtering method and 3.49 eV for the films prepared by the triode sputtering. This difference is defined by different deposition conditions such as the argon pressure, the applied sputtering voltage etc.

Various types of thin films were deposited to prepare ZnO nanostructures as shown in the flow chart (Figure 2) and in the (Table 1). First group of samples was grown on the gold round islands with diameter of 330 µm and with distance of 220 µm between islands, which were coated by the continuous Zn film. These samples were heated at atmospheric pressure and at temperature of 5500C during 5 hours. (Figure 5) represents high magnification SEM photography recorded on these samples after annealing with various magnification. The film’s surface was drastically changed after heating and optical photographs illustrate this claim very clear. Some bushes grown inside and around the gold islands are seen in these pictures. (Figures 5-a, 5-b and 5-c) present the SEM images with the scale of 100 µm, 1 µm and 200 nm respectively. As shown, the observed sample contains the nanostructure representing the chaotic arranged rod-like nanocrystals with length up to 7-10 microns and with thickness of 2-5 nm.

Figure 4: Optical transmittance of the ZnO films deposited on the glass substrate.

A B

C

Figure 5: First group samples recorded after annealing: Figs. 5-a, 5-b and 5-c present the SEM images.

Axelevitch A (2018) Investigation of nanogenerators composed of zinc oxide nanostructures prepared by thermal oxidation of metal zinc

Front Nanotechnol Volume 1(1): 20195

In the second group of samples, the gold sublayer was deposited through the strips shaped mask. Here, also continuous Zn film was deposited on the shaped gold surface. This group of samples was heated at 6000C during 5 hours at atmospheric pressure. (Figure 6) represents the high-resolution SEM photographs made on these samples after annealing with various magnification. SEM photographs of the samples after heating shown in (Figure. 6-a, 6-b and 6-c). As shown, in this case, changes in the film’s structure was more significant. Here, more part of the Zn layer was oxidized that leads to growth of more massive nanocrystals. However, in this case, the grown nanorods looks a little bit another. They

have different dimensions from the first samples, their length was of approximately 5-7 mm and their diameter was of ~ 100-150 nm. These nanorods are arranged perpendicularly to the origin surface. Thus, the annealing temperature significantly influences on the ZnO nanostructures growth.

In the third group of samples, the metal Zn was deposited through the same mask as in the first group, however the gold sublayer here represents the continuous thin film. In this case, the heating process was provided at temperature of 6500C during 5 hours. One can see that substantial changes have occurred in the Zn islands and in the vicinity. (Figure 7) represents SEM images recorded on these samples after

A B

Figure 6: Second group samples recorded after annealing: Figs. 6-a, 6-b and 6-c present the SEM images.

A B

C

Figure 7: Third group samples recorded after annealing: Figs. 7-a, 7-b and 7-c present the SEM images.

Axelevitch A (2018) Investigation of nanogenerators composed of zinc oxide nanostructures prepared by thermal oxidation of metal zinc

Front Nanotechnol Volume 1(1): 20196

annealing with various magnification and. (Figure 7-a) represents the SEM image of the sample with resolution of 100 µm. (Figures 7-b and 7-c) show the SEM images with the scale of 200 nm and 100 nm respectively. Number and length of nanorods relatively decreases, however their thickness increases up to 150-200 nm. Also, the flower-like structures appeared here.

Images, made using SEM, show that two types of ZnO nanostructures prevail here: the same nanorods as in the second group of samples and another type of nanocrystals shaped as shells or flower petals. However, these forms look more blurred and smoother than in the second group of samples. (Figure 8) illustrates these two groups of ZnO nanostructures obtained in the sample # 2. One group is the nanorods (see Figure 8-a) grown perpendicularly to the surface of the Zn layer in the delaminated part of the coating. This system consists of Au sublayer, Zn-origin layer and grown ZnO nanorods. ZnO nanorods represent crystals with length of several micron and thickness of one-two hundreds nanometers. Another type of ZnO nanostructures (see Figure 8-b) is the microcrystalline petals with dimensions of tens microns. It is interesting to note that more developed ZnO nanostructures had appeared at the cases of non-homogeneous sublayers. Two conditions should be observed to grow the developed nanostructure from metal Zn coating: the presence of a gold sublayer and existence of

inhomogeneities of the Au-Zn interfaces. So, the Au layer must be presented as small islands or nanoparticles. Applying of a more developed and heterogeneous ZnO nanostructure should lead to an increase in the generated electric power.

Electrical measurements of signals, produced by our nanogenerators, show that there are two different types of measured output voltage shapes as presented in figure 9. On both pictures, an upper signal represents a voltage applied to the standard transducer and lower signal is the voltage measured on the grown nanogenerator. (Figure 9-a) presents the voltage shape obtained from samples with high resistance between lower and upper electrodes. (Figure 9-b) shows the very noisy voltage shape measured on the samples with low resistance (short circuit). This difference may be explained by quality of the protecting dielectric film. Low resistance of the samples shows the low quality of the silicon monoxide film or delamination of one of the internal thin films.

Interesting to note, that in the case of low-resistance samples, the amplitude of the noisy signal is proportional to the applied force. These signals were rectified and measured. To rectify obtained signals, we tried to use standard PN diodes with the built-in potential around 0.7 V and low-noise Schottky diodes with the built-in potential of 0.34 V. Our measurements show that only Schottky diodes enable to obtain readable DC voltage.

A B

Figure 8: ZnO nanostructures grown on the Zn surface at 6000C: the nanorods structure (a) and the petals structure (b).

Figure 9: Measured input and output voltages: (a) samples with high resistance between electrodes, (b) samples with low resistance (short circuit) between electrodes.

Axelevitch A (2018) Investigation of nanogenerators composed of zinc oxide nanostructures prepared by thermal oxidation of metal zinc

Front Nanotechnol Volume 1(1): 20197

(Figure 10) represents dependence of the rectified output voltage measured on the four samples designated in Table 1 on the input voltage applied to the transducer. As shown in figure 10, the measured voltage increases linearly with increasing the input voltage which provides an acoustic signal. If we assume that our multilayer system represents a flat capacitor filled by a material with the piezoelectric properties, the charge accumulated by the capacitor will be equal to

Q = kF (1)

Where k is the piezoelectric coefficient and F is the force applied to the capacitor plates. On the other hand, the charge accumulated in the flat capacitor produce voltage on its plates which equal to:

(2)

Where C is the capacitance, d is the thickness of the piezoelectric material, A is the area of the capacitor and ε0 and εr are the permittivity of vacuum and the relative dielectric coefficient of the piezoelectric material respectively. Substituting of both relations, we obtain:

(3)

Therefore, the voltage generated by a such flat multilayer system will be linearly proportional to the applied force and vice versa. Abrupt increase in the range between 6 and 9 V in the Fig. 10 may be explained by difference in the contact potentials between lower and upper electrodes, gold and aluminum respectively. In other word, our devices represent the structure like to the MIM-diodes. The diode-type I-V characteristics were obtained also by growth of different types of ZnO nanostructures on the GaN substrates [29]. Our devices not contain semiconductors besides of ZnO, however we used different metals for electrodes. Evidently, this conclusion should be checked experimentally. Thus, the plots shown in Figure 10 properly reflects the piezoelectric properties of the grown multilayer systems. Therefore, the prepared samples containing unordered ZnO nanostructures can be used as the nanogenerators and acoustic sensors. We explain the difference in the samples behavior by differences of substrates and structures (see Table 1).

The follows plots, presented in (Figure 11), show dependence of output voltage on the input frequency of mechanical action. As known, the piezoelectric coefficient is approximately constant at low frequencies (0.2-1 kHz), if it is defined by the

Figure 10: Plot of the dependence of output voltage on the input voltage generated by the signal generator.

Figure 11: Plot of the dependence of output voltage on the excitation frequency.

Axelevitch A (2018) Investigation of nanogenerators composed of zinc oxide nanostructures prepared by thermal oxidation of metal zinc

Front Nanotechnol Volume 1(1): 20198

relation of displacement to the applied voltage [30]. Research, provided in the large range of frequencies shows that in the range up to 50 kHz, the relative permittivity of ZnO films slightly decrease and after that remains practically constant. At the same time, dielectric losses decrease approximately up to 10 kHz and after that its begin to grow [31]. Each curve shown in (Figure 11) presents different behavior under the same conditions. Here, the sample # 1 represents the system annealed at 5500C, samples # 2 and # 3 were annealed up to 6000C and 6500C respectively and forth sample was annealed up to 3000C. Equation 3 contains the piezoelectric constant in the numerator and the relative dielectric coefficient in the denominator. Both these parameters are defined by the structure of the grown films, by the substrate material and depend on the applied excitation frequency (Figure 11) shows measured results from different samples, therefore these results are different also. Thus, difference in the output voltage curves behavior is defined by various types of substrates and growth details.

Comparing of measured results with results of other authors shows that the voltage produced by our experimental piezoelectric devices is in the same range that results obtained and described in literature sources. To obtain the flexible nanogenerators, researchers have created nanoparticles by various methods and have mixed with some organic compounds. For example, ZnO nanoparticles were deposited by evaporation and mixed with a specific glue [6], grown by the hydrothermal method and dispersed in the polydimethylsiloxane (PDMS) [32], grown and mixed with the multiwall carbon nanotubes through the PDMS [33]. Moreover, the nanoparticles made from other piezoelectric materials were used for the nanogenerators preparation [34]. Measured voltage here was in the interval of 0.8 – 7.5 V. Therefore, the results obtained in our experiments can be considered satisfactory.

ConclusionsIn our work, it was confirmed that nano-structured ZnO crystals can be grown by annealing in an air atmosphere the Zn metal films deposited using vacuum evaporation method on the gold sublayer. Two various types of ZnO crystal forms were observed in our experiments, nano-rods and nano-petals. It was found that the more developed nanostructures grow on dislocations of the gold-zinc interfaces. Internal resistance of the prepared samples significantly influences on the produced electrical signal. Generated voltage of grown nanogenerators was from 0.4 V up to 1.3 V depending on the voltage applied to the exciting transducer. The multilayer systems based on the ZnO nano-structures enable to produce electricity under mechanical action. These systems are promising for the direct conversion of the mechanical vibration into the electricity.

Reference1. Elmer K, Klein A, Rech B (2007) Transparent Conductive Zinc

Oxide, Springer. [View Article]

2. Banerjee D, Jo SH, Ren ZF (2004) Adv. Mater. 22: 2028-2032. [View Article]

3. Chhikara D, Srivatsa KMK, Kumar MS, Singh P, Das S, et al. (2015) Growth and field emission properties of vertically-aligned ZnO nanowire array on biaxially textured Ni-W substrate by thermal evaporation, Adv. Mater. Lett. 10: 862-866. [View Article]

4. He J, Zheng X, Hong X, Wang W, Cao y et al (2018) Mater. Let. 216: 182-184. [View Article]

5. Muiva C, Sathiaraj TS, Maabong K (2012) Chemical Spray Pyrolysis Path to Synthesis of ZnO Micro sausages from Aggregation of Elongated Double Tipped Nanoparticles, Mater. Sci. Forum 706: 2577–2582. [View Article]

6. Al-Ruqeishi MS, Mohiuddin T, Al-Habsi B, Al-Ruqeishi F, Al-Fahdi A et al. (2016) Piezoelectric nanogenerator based on ZnO nanorods, Arab. J. Chem. [View Article]

7. Hossain MF, Zhang ZH, Takahashi T, (2010) Novel micro-rings tructured ZnO photoelectrode for dye-sensitized solar cell, Nano-Micro Lett 2: 53–55. [View Article]

8. Parkansky N, Shalev G, Alterkop B, Goldsmith S, Boxman RL, et al. (2006) Growth of ZnO nanorods by air annealing of ZnO films with an applied electric field, Surf Coat Tech. 201: 2844–2848. [View Article]

9. Wang ZL, (2004) Zinc oxide nanostructures: growth, properties and applications, J. Phys.-Condens. Mat. 16: R829–R858. [View Article]

10. Lovchinov K, Ganchev M, Petrov M, Nichev H, Dimova-Malinovska D et al. (2013) Electrochemically deposited nanostructured ZnO layers on the front side of c-Si solar cell, Bulg Chem Commun. 153–158. [View Article]

11. Qi H, Glaser ER, Caldwell JD, Prokes SM, (2012) Growth of Vertically Aligned ZnO Nanowire Arrays Using Bilayered Metal Catalysts, J. Nanomater. [View Article]

12. Muchuweni E, Sathiaraj TS, Nyakotyo H, (2017) Synthesis and characterization of zinc oxide thin films for optoelectronic applications, Helyion. [View Article]

13. Opoku C, Dahiya AS, Oshman C, Cayrel F, Poulin-Vittrant G et al. (2015) Fabrication of ZnO Nanowire Based Piezoelectric Generators and Related Structures, Phys. Proc. 70: 858 – 862. [View Article]

14. Kiriakidis G, Kortidis I, Cronin SD, Morris NJ, Cairns DR et al. (2014) Tribological investigation of piezoelectric ZnO films for rolling contact-based energy harvesting and sensing applications, Thin Solid Films 555: 68-75. [View Article]

15. Lv M, Xiu X, Pang Z, Dai Y, Han S (2005) Transparent conducting zirconium-doped zinc oxide films prepared by rf magnetron sputtering, Appl Surf Sci 252: 2006-2011. [View Article]

16. Lv M, Xiu X, Pang Z, Dai Y, Ye L et al. (2008) Structural, electrical and optical properties of zirconium-doped zinc oxide films prepared by radio frequency magnetron sputtering, Thin Solid Films 516: 2017-2021. [View Article]

17. Zhang HF, Lei CX, Liu HF, Yuan CK (2009) Low-temperature deposition of transparent conducting ZnO:Zr films on PET substrates by DC magnetron sputtering, Appl Surf Sci 255: 6054-6056.[View Article]

18. Xu S, Qin Y, Xu C, Wei Y, Yang R, et al. (2010) Self-powered nanowire devices, Nat. Nanotechnol. 5: 366–373. [View Article]

19. Roundy S, Wright PK (2004) A piezoelectric vibration based generator for wireless electronics, Smart Mater. Struct. 13: 1131–1142. [View Article]

Axelevitch A (2018) Investigation of nanogenerators composed of zinc oxide nanostructures prepared by thermal oxidation of metal zinc

Front Nanotechnol Volume 1(1): 20199

20. Sun C, Shi J, Wang X, (2010) Fundamental study of mechanical energy harvesting using piezoelectric nanostructures, J. Appl. Phys 108: 034309. [View Article]

21. Chen X, Xu S, Yao N, Shi Y (2010) 1.6 V nanogenerator for mechanical energy harvesting using PZT nanofibers. Nano Let. 10: 2133–2137. [View Article]

22. Hu Y, Lin L, Zhang Y, Wang ZL (2012) Replacing a battery by a nanogenerator with 20 V output. Adv. Mater 1: 110–114. [View Article]

23. Khanlary MR, Vahedi V, Reyhani A, (2012) Synthesis and Characterization of ZnO Nanowires by Thermal Oxidation of Zn Thin Films at Various Temperatures, Molecules 17: 5021-5029. [View Article]

24. Ching-Fu Lin, Liang-Chiun Chao (2010) ZnO Nanowires Prepared by Thermal Oxidation of Metallic Zinc Films, Proceeding of the 3rd International Nanoelectronics Conference (INEC), 1074-1075. [View Article]

25. Martinez O, Hortelano V, Jimenez J, Plaza JL, de Dios S et al. (2011) Growth of ZnO nanowires through thermal oxidation of metallic zinc films on CdTe substrates, J. Alloy. Compd. 509: 5400-5407. [View Article]

26. Golan G, Axelevitch A (2002) Novel method of low-vacuum plasma triode sputtering, Microelectron. J 33: 651-657. [View Article]

27. Axelevitch A, Gorenstein B, Darawshe H, Golan G (2010)

Investigation of thin solid ZnO films prepared by sputtering, Thin Solid Films 518: 4520-4524. [View Article]

28. Khelladi NB, Sari NEC (2013) Optical properties of ZnO thin films, Adv. Mater. Sci. 13: 21-29. [View Article]

29. Alvi NH, Usman Ali SM, Hussain S, Nur O, Willander M (2011) Fabrication and comparative optical characterization of n-ZnO nanostructures (nanowalls, nanorods, nanoflowers and nanotubes)/p-GaN white-light-emitting diodes, Scripta Mater. 64: 697-700. [View Article]

30. Zhanga K, Zhao Y, He F, Liu D (2007) Piezoelectricity of ZnO Films Prepared by Sol-Gel Method, Chin. J. Chem. Phys. 20: 721-726. [View Article]

31. Aleksandrova M, Kolev G, Vucheva Y, Pathan H, Denishev K (2017) Characterization of Piezoelectric Microgenerator with Nanobranched ZnO Grown on a Polymer Coated Flexible Substrate, Appl. Sci. [View Article]

32. Rahman W, Garain S, Sultana A, Middya TR, Mandal D (2018) Self-powered piezoelectric nanogenerator base on wurtzite ZnO nanoparticles for energy harvesting application, Materials Today, proc. 5: 9826-9830. [View Article]

33. Sun H, Tian H, Yang Y, Xie D, Zhang YC et al. (2013) A novel flexible nanogenerator made of ZnO nanoparticles and multiwall carbon nanotube, Nanoscale 5: 6117-6123. [View Article]

34. Song J, Zhao G, Li B, Wang J (2017) Design optimization of PVDF-based piezoelectric energy harvesters, Heliyon. [View Article]

Citation: Axelevitch A, Lapsker I (2019) Investigation of nanogenerators composed of zinc oxide nanostructures prepared by thermal oxidation of metal zinc. Front Nanotechnol 1: 001-009.

Copyright: © 2019 Axelevitch A, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.