- Nano Express
- Open Access
Synthesis and enhanced humidity detection response of nanoscale Au-particle-decorated ZnS spheres
© Liang and Liu; licensee Springer. 2014
- Received: 5 November 2014
- Accepted: 25 November 2014
- Published: 30 November 2014
We successfully prepared Au-nanoparticle-decorated ZnS (ZnS-Au) spheres by sputtering Au ultrathin films on surfaces of hydrothermally synthesized ZnS spheres and subsequently postannealed the samples in a high-vacuum atmosphere. The Au nanoparticles were distributed on ZnS surfaces without substantial aggregation. The Au nanoparticle diameter range was 5 to 10 nm. Structural information showed that the surface of the annealed ZnS-Au spheres became more irregular and rough. A humidity sensor constructed using the Au-nanoparticle-decorated ZnS spheres demonstrated a substantially improved response to the cyclic change in humidity from 11% relative humidity (RH) to 33% to 95% RH at room temperature. The improved response was associated with the enhanced efficiency of water molecule adsorption onto the surfaces of the ZnS because of the surface modification of the ZnS spheres through noble-metal nanoparticle decoration.
- Surface modification
Semiconducting compounds have been proposed as potential materials for use in sensing devices for gas detection and humidity measurement [1–4]. In particular, because of their high surface-to-volume ratio, nanostructured semiconductors exhibit physical and chemical behaviors that are superior to their bulk counterparts [5–7]. Among various sensors, humidity sensors have crucial applications in semiconductor electronics and food-processing industries. Various semiconducting materials have been used in humidity-sensing devices [8, 9]. The ZnS-based humidity sensors have been realized through complex processes or a high-temperature process [10, 11]. Humidity sensors based on ZnS with a facile synthesis methodology are limited in number. ZnS is one of the most crucial II to VI semiconductor compounds . ZnS has shown promise for use in novel diverse applications including light-emitting diodes, sensors, infrared windows, electroluminescent materials, and flat-panel displays [3, 12–15]. ZnS nanostructures can be synthesized by various physical and chemical methodologies [3, 16]. Although thermal evaporation has been widely used for synthesizing nanoscale ZnS, both the extremely high process temperature and complex process control prevent the realization of high-performance ZnS-based sensors . From a morphological perspective, enhancing the sensing performance of nanostructures continues to be challenging, despite their sensing properties being superior to those of thin films and bulk materials. Recently, surface functionalization with noble metals or through noble-metal doping has been achieved, and it enhances the sensitivity and stability of nanostructure-based sensors [17–19]. However, most of these studies have focused on gas-sensing behaviors, and there are few reports on the humidity-sensing behavior. Recently, Pd2+-doped ZnO nanotetrapods were prepared and the humidity detection capability of ZnO was improved through noble-metal doping . Room-temperature humidity-sensing properties of boron nitride nanotubes have been enhanced through surface decoration with Au particles . In this study, a combination of a chemical solution process and the sputtering technique was used to prepare Au-nanoparticle-decorated ZnS spheres. The effects of the surface modification of ZnS-based humidity sensors through Au-nanoparticle decoration were investigated in this study. The ZnS-based humidity sensor performance was observed to be correlated with microstructural changes.
The zinc nitrate (Zn(NO3)2 · 6H2O) and thioacetamide (TAA) were used as source materials to prepare hydrothermally synthesized ZnS spheres in this work . The polyvinylpyrrolidone (PVP) was used as a surfactant to control the ZnS sphere size. The 200-nm-thick SiO2/Si (100) substrates were used as templates for deposition of ZnS spheres. The reaction solution contains equimolar of zinc nitrate (0.05 M) and TAA (0.05 M). The PVP was subsequently added to the above solution. The reaction solution was stirred at room temperature for 30 min. Subsequently, the reaction solutions and the substrates were transferred into a Teflon-lined stainless steel autoclave. The hydrothermal reaction temperature was fixed at 130°C and the duration is 6 h. At the end of the growth period, the substrates were removed from the solution, then immediately rinsed with deionized water to remove any residual salt from the surface, and dried in air. For synthesis of Au-nanoparticle-decorated ZnS spheres, Au ultrathin film was deposited onto the surfaces of the hydrothermally synthesized ZnS spheres using a home-built DC sputtering system. During deposition, substrate temperature was maintained at room temperature, and the deposition gas pressure was fixed at 20 mTorr with a pure Ar ambient. The sputtering time and power for the Au are 40 s and 20 W, respectively. The samples were further annealed in a high vacuum chamber (base pressure approximately 3 × 10−6 Torr) at 300°C for 30 min to induce ultra-thin Au film to form Au nanoparticles on the ZnS surfaces (ZnS-Au). The 200-nm-thick SiO2 layer herein was used as an insulator layer. The ZnS and ZnS-Au spheres were dispersed onto the SiO2 layer. Subsequently, the silver glue was used to fabricate two metal electrodes onto the ZnS/SiO2 for electric measurements.
Crystal structures of the samples were investigated by X-ray diffraction (XRD; Panalytical X’Pert Pro MPD) using Cu Kα radiation. Morphologies of the as-synthesized samples were characterized by scanning electron microscopy (SEM; Hitachi S-4800), and high-resolution transmittance electron microscopy (HRTEM; Philips Tecnai F20 G2) was used to investigate the coverage and morphology of Au nanoparticles on the surfaces of the ZnS spheres. The energy-dispersive X-ray spectroscopy (EDS) attached to TEM was used to evaluate the composition of the samples. Room temperature-dependent photoluminescence (PL; JOBIN-YVON T64000 Micro-PL Spectroscopy) spectra were obtained using the 325-nm line of a He-Cd laser. The electrical characteristics of the ZnS-based sensors were tested as a function of relative humidity (RH) with a fixed applied voltage of 5 V in a home-built testing chamber at room temperature. A computer was used to collect the signals from the sensor in the testing circuit. The RH levels for the humidity sensor test herein were controlled to be approximately 11%, 33%, 55%, 75%, 85%, and 95% and a hygrometer was used to monitor RH levels in the test chamber. The experimental setup has been described elsewhere . The different RH levels were generated by referencing various saturated salt solutions in closed chamber at room temperature . The humidity sensitivity test of the samples was performed with the sample initially stored in the dry ambient (11% RH); subsequently, the sensor was upon exposure to one of the higher selected RH levels (33% to 95%). Finally, the sensor was restored in the 11% RH environment again to finish a test run.
Highly crystalline ZnS spheres were decorated with Au particles by combining the sputtering technique and high-vacuum thermal annealing. Detailed TEM images revealed that the as-synthesized Au particles had nanoscale sizes and that they were efficiently distributed on the surface of the ZnS spheres. PL spectra revealed that the nanoparticle surface modification changed the PL spectra intensity and intensity ratio of ZnS emission bands. Au nanoparticles decorating the surface of the ZnS spheres significantly affected the sensor’s humidity response. The ZnS-Au sensor exhibited considerably enhanced sensitivity compared with a pure ZnS sphere sensor at various percent RH levels operated at room temperature.
YCL is a professor of the Institute of Materials Engineering at National Taiwan Ocean University (Taiwan). SLL is a graduate student of the Institute of Materials Engineering at National Taiwan Ocean University (Taiwan).
This work is supported by the Ministry of Science and Technology of Taiwan (Grant No. NSC 102-2221-E-019-006-MY3).
- Kannan PK, Saraswathi R, Rayappan JBB: CO2 gas sensing properties of DC reactive magnetron sputtered ZnO thin film. Ceram Int 2014, 40: 13115–13122. 10.1016/j.ceramint.2014.05.011View ArticleGoogle Scholar
- Nenov T, Nenova Z: Multi-objective optimization of the parameters of TiO2-based ceramic humidity sensors. Ceram Int 2013, 39: 4465–4473. 10.1016/j.ceramint.2012.11.040View ArticleGoogle Scholar
- Reddy DA, Kim DH, Rhee SJ, Lee BW, Liu C: Tunable blue-green-emitting wurtzite ZnS:Mg nanosheet-assembled hierarchical spheres for near-UV white LEDs. Nanoscale Res Lett 2014, 9: 20. 10.1186/1556-276X-9-20View ArticleGoogle Scholar
- Liu Y, Li Z, Zhong W, Zhang L, Chen W, Li Q: Synthesis and photoluminescence properties of ZnS nanobowl arrays via colloidal monolayer template. Nanoscale Res Lett 2014, 9: 389. 10.1186/1556-276X-9-389View ArticleGoogle Scholar
- Zhang Y, Yu K, Jiang D, Zhu Z, Geng H, Luo L: Zinc oxide nanorod and nanowire for humidity sensor. Appl Surf Sci 2005, 242: 212–217. 10.1016/j.apsusc.2004.08.013View ArticleGoogle Scholar
- Liang YC, Lin TY: Fabrication and sensing behavior of one-dimensional ZnO-Zn2GeO4 heterostructures. Nanoscale Res Lett 2014, 9: 389. 10.1186/1556-276X-9-389View ArticleGoogle Scholar
- Li Z, Ding D, Liu Q, Ning C, Wang X: Ni-doped TiO2 nanotubes for wide-range hydrogen sensing. Nanoscale Res Lett 2014, 9: 118. 10.1186/1556-276X-9-118View ArticleGoogle Scholar
- Adhyapak PV, Kadam V, Mahadik U, Amalnerkar DP, Mulla IS: Influence of Li doping on the humidity response of maghemite (γ-Fe2O3) nanopowders synthesized at room temperature. Ceram Int 2013, 39: 8153–8158. 10.1016/j.ceramint.2013.03.089View ArticleGoogle Scholar
- Mattogno G, Righini G, Montesperelli G, Traversa E: XPS analysis of the interface of ceramic thin films for humidity sensors. Appl Surf Sci 1993, 70–71:Part 1: 363–366.View ArticleGoogle Scholar
- Zhang W, Feng C, Yang Z: An inward replacement/etching route to controllable fabrication of zinc sulfide nanotube arrays for humidity sensing. Sens Actuators B 2012, 165: 62–67. 10.1016/j.snb.2012.02.013View ArticleGoogle Scholar
- Üzar N, Okur S, Arıkan MÇ: Investigation of humidity sensing properties of ZnS nanowires synthesized by vapor liquid solid (VLS) technique. Sens Actuators A: Physical 2011, 167: 188–193. 10.1016/j.sna.2010.10.005View ArticleGoogle Scholar
- Hwang DH, Ahn JH, Hui KN, Hu KS, Son YG: Structural and optical properties of ZnS thin films deposited by RF magnetron sputtering. Nanoscale Res Lett 2012, 7: 26. 10.1186/1556-276X-7-26View ArticleGoogle Scholar
- Liu Y, He Y, Yuan Z, Zhu J, Han J: Numerical and experimental study on thermal shock damage of CVD ZnS infrared window material. J Alloys Compd 2014, 589: 101–108.View ArticleGoogle Scholar
- Yang H, Huang C, Su X, Tang A: Microwave-assisted synthesis and luminescent properties of pure and doped ZnS nanoparticles. J Alloys Compd 2005, 402: 274–277. 10.1016/j.jallcom.2005.04.150View ArticleGoogle Scholar
- Yang H, Yu S, Yan J, Zhang L: Random lasing action from randomly assembled ZnS nanosheets. Nanoscale Res Lett 2010, 5: 809–812. 10.1007/s11671-010-9563-8View ArticleGoogle Scholar
- Kar S, Chaudhuri S: Controlled synthesis and photoluminescence properties of ZnS nanowires and nanoribbons. J Phys Chem B 2005, 109: 3298–3302. 10.1021/jp045817jView ArticleGoogle Scholar
- Liang Y-C, Liao W-K, Deng X-S: Synthesis and substantially enhanced gas sensing sensitivity of homogeneously nanoscale Pd- and Au-particle decorated ZnO nanostructures. J Alloys Compd 2014, 599: 87–92.View ArticleGoogle Scholar
- Chang C-M, Hon M-H, Leu I-C: Improvement in CO sensing characteristics by decorating ZnO nanorod arrays with Pd nanoparticles and the related mechanisms. RSC Adv 2012, 2: 2469. 10.1039/c2ra01016jView ArticleGoogle Scholar
- Hongsith N, Viriyaworasakul C, Mangkorntong P, Mangkorntong N, Choopun S: Ethanol sensor based on ZnO and Au-doped ZnO nanowires. Ceram Int 2008, 34: 823–826. 10.1016/j.ceramint.2007.09.099View ArticleGoogle Scholar
- Wang X, Zhang J, Zhu Z, Zhu J: Humidity sensing properties of Pd2+-doped ZnO nanotetrapods. Appl Surf Sci 2007, 253: 3168–3173. 10.1016/j.apsusc.2006.07.033View ArticleGoogle Scholar
- Yu Y, Chen H, Liu Y, Li LH, Chen Y: Humidity sensing properties of single Au-decorated boron nitride nanotubes. Electrochem Commun 2013, 30: 29–33.View ArticleGoogle Scholar
- Yan X, Michael E, Komarneni S, Brownson JR, Yan Z-F: Microwave- and conventional-hydrothermal synthesis of CuS, SnS and ZnS: optical properties. Ceram Int 2013, 39: 4757–4763. 10.1016/j.ceramint.2012.11.062View ArticleGoogle Scholar
- Liang Y-C, Liao W-K, Liu S-L: Performance enhancement of humidity sensors made from oxide heterostructure nanorods via microstructural modifications. RSC Adv 2014, 4: 50866–50872. 10.1039/C4RA05301JView ArticleGoogle Scholar
- Lu Y, Wang Z, Yuan S, Shi L, Zhao Y, Deng W: Microwave-hydrothermal synthesis and humidity sensing behavior of ZrO2 nanorods. RSC Adv 2013, 3: 11707. 10.1039/c3ra40670aView ArticleGoogle Scholar
- Dunstan DE, Hagfeldt A, Almgren M, Siegbahn HOG, Mukhtar E: Importance of surface reactions in the photochemistry of zinc sulfide colloids. J Phys Chem 1990, 94: 6797–6804. 10.1021/j100380a048View ArticleGoogle Scholar
- Wang Y, Zhang L, Liang C, Wang G, Peng X: Catalytic growth and photoluminescence properties of semiconductor single-crystal ZnS nanowires. Chem Phys Lett 2002, 357: 314–318. 10.1016/S0009-2614(02)00530-4View ArticleGoogle Scholar
- Zhou XT, Kim PSG, Sham TK, Lee ST: Fabrication, morphology, structure, and photoluminescence of ZnS and CdS nanoribbons. J Appl Phys 2005, 98: 024312. 10.1063/1.1988974View ArticleGoogle Scholar
- Liu YG, Feng P, Xue XY, Shi SL, Fu XQ, Wang C, Wang YG, Wang TH: Room-temperature oxygen sensitivity of ZnS nanobelts. Appl Phys Lett 2007, 90: 042109. 10.1063/1.2432278View ArticleGoogle Scholar
- Kulwicki BM: Humidity sensors. J Am Ceramic Soc 1991, 74: 697–708. 10.1111/j.1151-2916.1991.tb06911.xView ArticleGoogle Scholar
- Erol A, Okur S, Comba B, Mermer Ö, Arıkan MÇ: Humidity sensing properties of ZnO nanoparticles synthesized by sol–gel process. Sens Actuators B 2010, 145: 174–180. 10.1016/j.snb.2009.11.051View ArticleGoogle Scholar
- Cao AM, Hu JS, Liang HP, Wan LJ: Self-assembled vanadium pentoxide (V2O5) hollow microspheres from nanorods and their application in lithium-ion batteries. Angew Chem Int Ed Engl 2005, 44: 4391–4395. 10.1002/anie.200500946View ArticleGoogle Scholar
- Tai W-P, Oh J-H: Fabrication and humidity sensing properties of nanostructured TiO2–SnO2 thin films. Sens Actuators B Chemical 2002, 85: 154–157. 10.1016/S0925-4005(02)00074-6View ArticleGoogle Scholar
- Su P-G, Shiu C-C: Electrical and sensing properties of a flexible humidity sensor made of polyamidoamine dendrimer-Au nanoparticles. Sens Actuators B 2012, 165: 151–156. 10.1016/j.snb.2012.02.032View ArticleGoogle Scholar
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