Characterization of Gold-Sputtered Zinc Oxide Nanorods—a Potential Hybrid Material
© Perumal et al. 2016
Received: 6 October 2015
Accepted: 6 January 2016
Published: 19 January 2016
Generation of hybrid nanostructures has been attested as a promising approach to develop high-performance sensing substrates. Herein, hybrid zinc oxide (ZnO) nanorod dopants with different gold (Au) thicknesses were grown on silicon wafer and studied for their impact on physical, optical and electrical characteristics. Structural patterns displayed that ZnO crystal lattice is in preferred c-axis orientation and proved the higher purities. Observations under field emission scanning electron microscopy revealed the coverage of ZnO nanorods by Au-spots having diameters in the average ranges of 5–10 nm, as determined under transmission electron microscopy. Impedance spectroscopic analysis of Au-sputtered ZnO nanorods was carried out in the frequency range of 1 to 100 MHz with applied AC amplitude of 1 V RMS. The obtained results showed significant changes in the electrical properties (conductance and dielectric constant) with nanostructures. A clear demonstration with 30-nm thickness of Au-sputtering was apparent to be ideal for downstream applications, due to the lowest variation in resistance value of grain boundary, which has dynamic and superior characteristics.
KeywordsZinc oxide Gold Nanorods Dopant Impedance Nanostructure
Advances in nanotechnological approaches have provided an insight to nanocreations and manipulation of various nanomaterials to yield unique metal nanostructures having interesting properties and functions [1–3]. In the past, special attentions have been paid to make nanostructures for fine-tuning their properties towards the development of sensing substrates [4–6]. Among the different nanohybrid structures, involvements of metal oxides have elevated a step ahead in different applications [7–10]. Nanoparticle made from metal oxides proved for their participation in sensing applications, especially for bio-recognition [11, 12]. Oxide groups reside in the nanomaterials/nanoparticle prepared by metal oxide impart improvement in sensitivity of biosensors . With the explored metal oxides, zinc oxide (ZnO)-based nanostructures have recently been aroused much interest due to its unique optical and electrical properties [14, 15].
ZnO has been widely used as material for semiconductor, because of its appealing characteristics, such as large exciton binding energy (60 meV). Special interests with ZnO usage have been taken to be used for electro-optical devices. Moreover, due to low cost, simplicity in fabrication and high electron mobility, optoelectronic devices rely on ZnO nanostructures (nanorods, nanowires and nanoflowers) [16–18]. Additionally, ZnO is stable at low and higher pH extremes and an ideal material for functionalization with biological and chemical compounds [11, 15]. With a property of excellent surface-to-volume ratio, ZnO nanohybrid has considered for improved catalytic activity. On the other hand, metal particles such as gold nanoparticle (AuNP) are shown to have high electron affinity; between AuNP and metal oxides, high Schottky barrier can be produced [19, 20]. Similar to ZnO, Au has been accepted as suitable material for biocompatibility, high conductivity and surface chemical functionalization [21–23]. Considering all these vital things, it is a wise approach to make ZnO and Au hybrid for creating nanostructures to be used for a wide range of applications.
In general, there are two major techniques that have been in nanofabrication of metal oxide nanostructures: “top-down” and “bottom-up”. Top-down approach is not a promising method because it contains some limitations such as low yield assembly, large-scale uniformity and repeatability issues, whereas bottom-up approach owns its superiority compared to top-down approach in terms of photolithography and is capable of producing various nanostructures with high yield, less defect and better range ordering . ZnO nanostructures prepared by bottom-up approach are catalytically synthesized by chemical vapour deposition (CVD) and vapour liquid solid (VLS) methods, where structures are assembled from their atomic level [24, 25]. Hence, ZnO nanostructure from bottom-up fabrication approaches has been preferred as it possesses unique physical, optical and electrical properties, which are highly suitable for downstream applications.
In the present study, we demonstrated a simple and facile route to synthesis Au-sputtered ZnO nanorods, and the thickness of Au-sputtering is tuned to investigate physical, optical and electrical properties of ZnO nanorods on the interdigitated electrode (IDE). Currently, there are only limited numbers of research articles highlighting the impedance spectroscopic analyses on hybrid materials. Herein, impedance spectroscopy tool was employed to investigate on Au-sputtered ZnO nanohybrid. By the addition of AuNPs to ZnO nanostructures, it leads changes in conduction and polarization mechanism, which are clearly addressed.
Au-Interdigitated Electrode Fabrication
ZnO Nanorods Synthesis
ZnO nanorods (ZnO-NRs) were prepared as described in our previous report . Briefly, 8.78 g of Zn(CH3COO)2·2H2O (98 %; Sigma-Aldrich) was dissolved in 200 ml of ethanol solvent (EtOH; 99.99 %; J.T. Baker) (ZnO seed solution solgel). The concentration of ZnO was kept constant as 0.2 M. The mixed solution was then vigorously stirred with a magnetic stirrer at 60 °C for 30 min. The stabilizer, monoethanolamine (MEA; 99 %; Merck), was added drop by drop to the ZnO solution with constant stirring for 2 h. Finally, the transparent and homogenous solution was stored for aging at room temperature. The aged ZnO solgel was deposited on the IDE device by using a spin coating technique at a speed of 3000 rpm for 20 s. The deposition process of the seed layer was repeated for three times to get a thicker ZnO thin film. For each deposition process, the coated ZnO thin films were dried at 150 °C for 20 min to remove the organic residuals that might exist on the ZnO thin films. The coated ZnO thin films were then annealed in a furnace under ambient air at 300 °C for 2 h to get highly crystallized ZnO. For the hydrothermal growth of ZnO nanofilm, the prepared substrate with the coated seed layer was submerged backward inside the growth solution using a Teflon sample holder. Equal concentration (25 mM) growth solution was prepared by mixing both zinc nitrate hexahydrate (99 %; Sigma-Aldrich) and hexamethylenetetramine (99 %; Merck) in deionized water. The growth process was completed inside an oven at 93 °C for 5 h. The prepared hydrothermally grown ZnO nanofilm was cleaned with isopropanol and deionized water to remove residual salts prior to annealing in a furnace under ambient air at 300 °C for 2 h.
Au-Decorated ZnO Nanorods Preparation
ZnO-NR-Au nanohybrids were prepared using a sputtering method. To form the ZnO-NR-Au nanohybrids, 10, 20, 30 and 40 nm Au wetting layers were physically deposited by a sputter coater (EMS550X) with Au target and a rotating stage. The detailed experimental conditions were as follows: electric current was maintained at 25 mA for 2–8 min with vacuum pressure of argon process level at 10−2 mbar. This process allowed us to obtain Au-decorated ZnO-NR forming ZnO-NR-Au nanohybrids. Figure 1a–d shows the schematic illustration of steps involved in the synthesis of Au IDE coated with Au-sputtered ZnO-NRs.
ZnO-NR-Au Hybrids Material Characterization
The morphology and structural properties of ZnO-NR-Au nanohybrid samples were investigated under field emission scanning electron microscopy (FESEM; Carl Zeiss AG ULTRA55, Gemini). High-resolution transmission electron microscopy (HRTEM) image and selected area electron diffraction pattern (SAED) of ZnO-NR-Au nanohybrids were acquired using PHILIPS, CM-200 TWIN with an incident energy 200 keV. X-ray diffraction (XRD; Bruker D8, Bruker AXS, Inc., Madison, WI, USA) with a Cu Kα radiation (λ = 1.54 Ǻ) was used to study the crystallization and structural properties of the ZnO-NR-Au nanohybrids. The material composition was analysed using X-ray photoelectron spectroscopy (XPS) (Omicron Dar400, Omicron, Germany). The chamber pressure was maintained at 2.4e−10 Torr throughout the measurement. The obtained peak was deconvolution using CasaXPS software. In addition, the optical and luminescence properties of ZnO-NR-Au nanohybrids were studied through photoluminescence (PL; Horiba Fluorolog-3, HORIBA Jobin Yvon Inc., USA). The PL spectra of the sample were recorded at different angles and positions to assure the result is not influenced by sample non-homogeneity. The impedance spectroscopy measurements were taken with applied AC amplitude of 1 V RMS in the frequency range of 1 Hz to 100 MHz using Novocontrol Alpha high-frequency analyser (Hundsangen, Germany). All the measurements were performed at room temperature.
Results and Discussion
Morphological Features of Au-Sputtered ZnO Thin Film
Parameters for ZnO nanorods sputtered with different Au thicknesses
ZnO/Au 10 nm
ZnO/Au 20 nm
ZnO/Au 30 nm
ZnO/Au 40 nm
ZnO-Au hybrid nanorods were grown successfully using hydrothermal method sputtered with different thicknesses of Au and have superior structural, optical and electrical characteristics compared to bare ZnO-NRs. Complete characterization of this structure was clearly demonstrated for their ultimate high-performance sensing. To investigate the effect of sputtered AuNP layers on the conduction mechanism, AC impedance spectroscopic analyses were performed. The results showed that the impedance and dielectric constant were decreased with the thickness of AuNP seeding increased. These variations were attributed to the grain sizes and dipole dynamics . A clear demonstration was shown with 30 nm thickness of Au, has a lowest variation in resistance value of grain boundary compared to other sizes fabricated, to be an optimal material for sensor. This study has shown an optimized ZnO/Au nanohybrid with complete characterizations, a tailored nanomaterial for downstream applications.
The authors would like to thank the Ministry of Higher Education Malaysia for the financial support through MTUN-COE grant 9016-00004 to conduct the research. The authors thank the Universiti Malaysia Perlis (UniMAP) for the opportunities to conduct the research in the Nano Biochip Lab, Failure Analysis Lab and Microfabrication Cleanroom. The authors thank Yaleeni Kanna Dasan from the Universiti Teknologi Petronas for the technical support. Appreciation is also due to all the team members and staff in the Department of Biotechnology; the Asian Institute of Medicine, Science and Technology University (AIMST); and the Institute of Nano Electronic Engineering (INEE) and School of Microelectronic Engineering (SoME), UniMAP.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Gopinath SCB, Awazu K, Fons P et al (2009) A sensitive multilayered structure suitable for biosensing on the BioDVD platform. Anal Chem 81:4963–4970. doi:https://doi.org/10.1021/ac802757z View ArticleGoogle Scholar
- Shima T, Gopinath SCB, Fujimaki M, Awazu K (2013) Detection and two-dimensional imaging of Escherichia coli attached to an optical disk. Jpn J Appl Phys 52:108004. doi:https://doi.org/10.7567/JJAP.52.108004 View ArticleGoogle Scholar
- Perumal V, Hashim U, Gopinath SCB et al (2015) A new nano-worm structure from gold-nanoparticle mediated random curving of zinc oxide nanorods. Biosens Bioelectron 78:14–22. doi:https://doi.org/10.1016/j.bios.2015.10.083 View ArticleGoogle Scholar
- Fujimaki M, Nomura K, Sato K et al (2010) Detection of colored nanomaterials using evanescent field-based waveguide sensors. Opt Express 18:15732–15740. doi:https://doi.org/10.1364/OE.18.015732 View ArticleGoogle Scholar
- Gopinath SCB, Awazu K, Fujimaki M et al (2008) Influence of nanometric holes on the sensitivity of a waveguide-mode sensor: label-free nanosensor for the analysis of RNA aptamer-ligand interactions. Anal Chem 80:6602–6609. doi:https://doi.org/10.1021/ac800767s View ArticleGoogle Scholar
- Gopinath SCB, Awazu K, Fujimaki M (2012) Waveguide-mode sensors as aptasensors. Sensors 12:2136–2151. doi:https://doi.org/10.3390/s120202136 View ArticleGoogle Scholar
- Jiang R, Li B, Fang C, Wang J (2014) Metal/semiconductor hybrid nanostructures for plasmon-enhanced applications. Adv Mater 26:5274–5309. doi:https://doi.org/10.1002/adma.201400203 View ArticleGoogle Scholar
- Wang FH, Yang CF, Lee YH (2014) Deposition of F-doped ZnO transparent thin films using ZnF2-doped ZnO target under different sputtering substrate temperatures. Nanoscale Res Lett 9:1–7. doi:https://doi.org/10.1186/1556-276X-9-97 View ArticleGoogle Scholar
- Dasan YK, Bhat AH, Faiz A (2015) Morphological and spectroscopic analysis of cellulose nanocrystals extracted from oil palm empty fruit bunch fiber. AIP Conf Proc 1669:76. doi:https://doi.org/10.1063/1.4919196 Google Scholar
- Perumal V, Hashim U (2013) Advances in biosensors: principle, architecture and applications. J Appl Biomed 11:1–34. doi:https://doi.org/10.1016/j.jab.2013.02.001 View ArticleGoogle Scholar
- Shi X, Gu W, Li B et al (2013) Enzymatic biosensors based on the use of metal oxide nanoparticles. Microchim Acta 181:1–22. doi:https://doi.org/10.1007/s00604-013-1069-5 View ArticleGoogle Scholar
- Balakrishnan SR, Hashim U, Gopinath SCB et al (2015) A point-of-care immunosensor for human chorionic gonadotropin in clinical urine samples using a cuneated polysilicon nanogap lab-on-chip. PLoS One 10:e0137891. doi:https://doi.org/10.1371/journal.pone.0137891 View ArticleGoogle Scholar
- Solanki PR, Kaushik A, Agrawal VV, Malhotra BD (2011) Nanostructured metal oxide-based biosensors. NPG Asia Mater 3:17–24. doi:https://doi.org/10.1038/asiamat.2010.137 View ArticleGoogle Scholar
- Perumal V, Hashim U, Gopinath SCB et al (2015) “Spotted nanoflowers”: gold-seeded zinc oxide nanohybrid for selective bio-capture. Sci Rep 5:12231. doi:https://doi.org/10.1038/srep12231 View ArticleGoogle Scholar
- Haarindraprasad R, Hashim U, Gopinath SCB et al (2015) Low temperature annealed zinc oxide nanostructured thin film-based transducers: characterization for sensing applications. PLoS One 10:1–20. doi:https://doi.org/10.1371/journal.pone.0132755 View ArticleGoogle Scholar
- Mishra YK, Modi G, Cretu V et al (2015) Direct growth of freestanding ZnO tetrapod networks for multifunctional applications in photocatalysis, UV photodetection, and gas sensing. ACS Appl Mater Interfaces 7:14303–14316. doi:https://doi.org/10.1021/acsami.5b02816 View ArticleGoogle Scholar
- Kashif M, Usman Ali SM, Ali ME et al (2012) Morphological, optical, and Raman characteristics of ZnO nanoflakes prepared via a sol–gel method. Phys Status Solidi 209:143–147. doi:https://doi.org/10.1002/pssa.201127357 View ArticleGoogle Scholar
- Humayun Q, Kashif M, Hashim U, Qurashi A (2014) Selective growth of ZnO nanorods on microgap electrodes and their applications in UV sensors. Nanoscale Res Lett 9:29. doi:https://doi.org/10.1186/1556-276X-9-29 View ArticleGoogle Scholar
- Jain PK, El-Sayed IH, El-Sayed MA (2007) Au nanoparticles target cancer. Nanotoday 2:18–29View ArticleGoogle Scholar
- Su L, Qin N (2015) A facile method for fabricating Au-nanoparticles-decorated ZnO nanorods with greatly enhanced near-band-edge emission. Ceram Int 41:2673–2679. doi:https://doi.org/10.1016/j.ceramint.2014.10.081 View ArticleGoogle Scholar
- Yuan YJ, Gopinath SCB, Kumar PKR (2011) Regeneration of commercial Biacore chips to analyze biomolecular interactions. Opt Eng 50:034402–1–6. doi:https://doi.org/10.1117/1.3554392 View ArticleGoogle Scholar
- Gopinath SCB, Lakshmipriya T, Awazu K (2014) Colorimetric detection of controlled assembly and disassembly of aptamers on unmodified gold nanoparticles. Biosens Bioelectron 51:115–123. doi:https://doi.org/10.1016/j.bios.2013.07.037 View ArticleGoogle Scholar
- Upadhyayula VKK (2012) Functionalized gold nanoparticle supported sensory mechanisms applied in detection of chemical and biological threat agents: a review. Anal Chim Acta 715:1–18. doi:https://doi.org/10.1016/j.aca.2011.12.008 View ArticleGoogle Scholar
- Foo KL, Hashim U, Muhammad K, Voon CH (2014) Sol-gel synthesized zinc oxide nanorods and their structural and optical investigation for optoelectronic application. Nanoscale Res Lett 9:1–10View ArticleGoogle Scholar
- Foo KL, Kashif M, Hashim U (2013) Study of zinc oxide films on SiO2/Si substrate by sol-gel spin coating method for pH measurement. Appl Mech Mater 284–287:347–351. doi:https://doi.org/10.4028/www.scientific.net/AMM.284-287.347 View ArticleGoogle Scholar
- Balakrishnan SR, Hashim U, Letchumanan GR et al (2014) Development of highly sensitive polysilicon nanogap with APTES/GOx based lab-on-chip biosensor to determine low levels of salivary glucose. Sensors Actuators A Phys 220:101–111. doi:https://doi.org/10.1016/j.sna.2014.09.027 View ArticleGoogle Scholar
- Balakrishnan SR, Hashim U, Gopinath SCB, et al. (2015) Polysilicon nanogap lab-on-chip facilitates multiplex analyses with single analyte. Biosens Bioelectron. doi: https://doi.org/10.1016/j.bios.2015.10.075
- Perumal V, Prasad RH, Hashim U (2013) pH measurement using in house fabricated interdigitated capacitive transducer. RSM2013 Proc. 2013, Langkawi, Malaysia, pp 33–36Google Scholar
- Wu J-J, Tseng C-H (2006) Photocatalytic properties of nc-Au/ZnO nanorod composites. Appl Catal B Environ 66:51–57. doi:https://doi.org/10.1016/j.apcatb.2006.02.013 View ArticleGoogle Scholar
- Mishra YK, Chakravadhanula VSK, Hrkac V et al (2012) Crystal growth behaviour in Au-ZnO nanocomposite under different annealing environments and photoswitchability. J Appl Phys 112:064308–1–5. doi:https://doi.org/10.1063/1.4752469 Google Scholar
- Strunk J, Kähler K, Xia X et al (2009) Au/ZnO as catalyst for methanol synthesis: the role of oxygen vacancies. Appl Catal A Gen 359:121–128. doi:https://doi.org/10.1016/j.apcata.2009.02.030 View ArticleGoogle Scholar
- Tan ST, Chen BJ, Sun XW et al (2005) Blueshift of optical band gap in ZnO thin films grown by metal-organic chemical-vapor deposition. J Appl Phys 98:013505–1–5. doi:https://doi.org/10.1063/1.1940137 Google Scholar
- Guo J, Zhang J, Zhu M et al (2014) Sensors and actuators B: chemical high-performance gas sensor based on ZnO nanowires functionalized by Au nanoparticles. Sensors Actuators B Chem 199:339–345View ArticleGoogle Scholar
- Kahraman S, Çakmak HM, Çetinkaya S et al (2013) Characteristics of ZnO thin films doped by various elements. J Cryst Growth 363:86–92. doi:https://doi.org/10.1016/j.jcrysgro.2012.10.018 View ArticleGoogle Scholar
- Wang X, Zhang X, Cheng W et al (2014) Facile synthesis and optical properties of polymer-laced ZnO-Au hybrid nanoparticles. Nanoscale Res Lett 9:1–7. doi:https://doi.org/10.1186/1556-276X-9-109 View ArticleGoogle Scholar
- Mishra YK, Mohapatra S, Singhal R et al (2008) Au-ZnO: a tunable localized surface plasmonic nanocomposite. Appl Phys Lett 92:043107–1–3. doi:https://doi.org/10.1063/1.2838302 View ArticleGoogle Scholar
- Tarwal NL, Devan RS, Ma YR et al (2012) Spray deposited localized surface plasmonic Au-ZnO nanocomposites for solar cell application. Electrochim Acta 72:32–39. doi:https://doi.org/10.1016/j.electacta.2012.03.135 View ArticleGoogle Scholar
- Gogurla N, Sinha AK, Santra S et al (2014) Multifunctional Au-ZnO plasmonic nanostructures for enhanced UV photodetector and room temperature NO sensing devices. Sci Rep 4:6483. doi:https://doi.org/10.1038/srep06483 View ArticleGoogle Scholar
- Tarwal NL, Rajgure a V, Inamdar a I et al (2013) Growth of multifunctional ZnO thin films by spray pyrolysis technique. Sensors Actuators A Phys 199:67–73. doi:https://doi.org/10.1016/j.sna.2013.05.003 View ArticleGoogle Scholar
- Kashif M, Ali ME, Ali SMU, Hashim U (2013) Sol–gel synthesis of Pd doped ZnO nanorods for room temperature hydrogen sensing applications. Ceram Int 39:6461–6466. doi:https://doi.org/10.1016/j.ceramint.2013.01.075 View ArticleGoogle Scholar
- Shinde SS, Korade a P, Bhosale CH, Rajpure KY (2013) Influence of tin doping onto structural, morphological, optoelectronic and impedance properties of sprayed ZnO thin films. J Alloys Compd 551:688–693. doi:https://doi.org/10.1016/j.jallcom.2012.11.057 View ArticleGoogle Scholar
- Xu Y, Yao B, Li YF et al (2014) Chemical states of gold doped in ZnO films and its effect on electrical and optical properties. J Alloys Compd 585:479–484. doi:https://doi.org/10.1016/j.jallcom.2013.09.199 View ArticleGoogle Scholar
- Hosseini ZS, Mortezaali A, Iraji A, Fardindoost S (2015) Sensitive and selective room temperature H2S gas sensor based on Au sensitized vertical ZnO nanorods with flower-like structures. J Alloys Compd 628:222–229View ArticleGoogle Scholar
- Mohapatra S, Mishra YK, Avasthi DK et al (2008) Synthesis of gold-silicon core-shell nanoparticles with tunable localized surface plasmon resonance. Appl Phys Lett 92:103105–1–3. doi:https://doi.org/10.1063/1.2894187 View ArticleGoogle Scholar
- Singh S, Zack J, Kumar D et al (2010) DNA hybridization on silicon nanowires. Thin Solid Films 519:1151–1155. doi:https://doi.org/10.1016/j.tsf.2010.08.060 View ArticleGoogle Scholar
- Wustoni S, Hideshima S, Kuroiwa S, Nakanishi T (2014) Sensitive electrical detection of human prion proteins using field effect transistor biosensor with dual-ligand binding amplification. Biosens Bioelectron 1–7. doi: https://doi.org/10.1016/j.bios.2014.08.028
- Jin X, Götz M, Wille S et al (2013) A novel concept for self-reporting materials: stress sensitive photoluminescence in ZnO tetrapod filled elastomers. Adv Mater 25:1342–1347. doi:https://doi.org/10.1002/adma.201203849 View ArticleGoogle Scholar
- Fabbri F, Villani M, Catellani A et al (2014) Zn vacancy induced green luminescence on non-polar surfaces in ZnO nanostructures. Sci Rep 4:5158. doi:https://doi.org/10.1038/srep05158 Google Scholar
- Lai CW, An J, Ong HC (2005) Surface-plasmon-mediated emission from metal-capped ZnO thin films. Appl Phys Lett 86:251105–1–3. doi:https://doi.org/10.1063/1.1954883 Google Scholar
- Lin J-H, Patil R a, Devan RS et al (2014) Photoluminescence mechanisms of metallic Zn nanospheres, semiconducting ZnO nanoballoons, and metal-semiconductor Zn/ZnO nanospheres. Sci Rep 4:6967. doi:https://doi.org/10.1038/srep06967 View ArticleGoogle Scholar
- Shao D, Sun H, Yu M et al (2012) Enhanced ultraviolet emission from poly(vinyl alcohol) ZnO nanoparticles using a SiO2-Au core/shell structure. Nano Lett 12:5840–5844View ArticleGoogle Scholar
- Park S, Mun Y, An S et al (2014) Enhanced photoluminescence of Au-functionalized ZnO nanorods annealed in a hydrogen atmosphere. J Lumin 147:5–8. doi:https://doi.org/10.1016/j.jlumin.2013.10.044 View ArticleGoogle Scholar
- Khoa NT, Kim SW, Yoo D-H et al (2015) Fabrication of Au/graphene-wrapped ZnO-nanoparticle-assembled hollow spheres with effective photoinduced charge transfer for photocatalysis. ACS Appl Mater Interfaces 7:3524–3531. doi:https://doi.org/10.1021/acsami.5b00152 Google Scholar
- Lin HY, Cheng CL, Chou YY et al (2006) Enhancement of band gap emission stimulated by defect loss. Opt Express 14:2372–2379. doi:https://doi.org/10.1364/OE.14.002372 View ArticleGoogle Scholar
- Rouhi J, Mamat MH, Ooi CHR et al (2015) High-performance dye-sensitized solar cells based on morphology-controllable synthesis of ZnO–ZnS heterostructure nanocone photoanodes. PLoS One 10:1–14. doi:https://doi.org/10.1371/journal.pone.0123433 View ArticleGoogle Scholar
- Cheng CW, Sie EJ, Liu B et al (2010) Surface plasmon enhanced band edge luminescence of ZnO nanorods by capping Au nanoparticles. Appl Phys Lett 96:3–5. doi:https://doi.org/10.1063/1.3323091 Google Scholar
- Saif AA, Poopalan P (2011) Correlation between the chemical composition and the conduction mechanism of barium strontium titanate thin films. J Alloys Compd 509:7210–7215. doi:https://doi.org/10.1016/j.jallcom.2011.04.068 View ArticleGoogle Scholar
- Srivastava S, Srivastava AK, Singh P et al (2015) Synthesis of zinc oxide (ZnO) nanorods and its phenol sensing by dielectric investigation. J Alloys Compd 644:597–601. doi:https://doi.org/10.1016/j.jallcom.2015.04.220 View ArticleGoogle Scholar
- Kashif M, Ali ME, Ali SMU et al (2013) Impact of hydrogen concentrations on the impedance spectroscopic behavior of Pd-sensitized ZnO nanorods. Nanoscale Res Lett 8:1–9. doi:https://doi.org/10.1186/1556-276X-8-68 View ArticleGoogle Scholar
- Alaeddin AS, Poopalan P (2010) Impedance/modulus analysis of sol–gel Ba_xSr_1-xTiO_3 thin films. J Korean Phys Soc 57:1449–1455. doi:https://doi.org/10.3938/jkps.57.1449 View ArticleGoogle Scholar
- Wang X, Kong X, Yu Y, Zhang H (2007) Synthesis and characterization of water-soluble and bifunctional ZnO-Au nanocomposites. J Phys Chem C 111:3836–3841View ArticleGoogle Scholar
- Shan G, Zhong M, Wang S et al (2008) The synthesis and optical properties of the heterostructured ZnO/Au nanocomposites. J Colloid Interface Sci 326:392–395. doi:https://doi.org/10.1016/j.jcis.2008.06.027 View ArticleGoogle Scholar