Synthesis of highly size confined ZnS quantum dots and its functional characteristics M. Navaneethan a , J. Archana a , K.D. Nisha b , Y. Hayakawa a , S. Ponnusamy c, ⁎, C. Muthamizhchelvan c a Research Institute of Electronics, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu, Shizuoka 432-8011, Japan b Department of Physics, Asan Memorial College of Engineering and Technology, Chengalpattu, 603105, Tamil Nadu, India c Department of Physics, SRM University, Kattankulathur, 603 203, Kancheepuram (D.t), Tamil Nadu, India abstract article info Article history: Received 15 September 2011 Accepted 13 October 2011 Available online 19 October 2011 Keywords: Semiconductors Optical materials and properties Nanocrystalline materials Solar energy materials ZnS quantum dots have been synthesized at room temperature using N-Methylaniline by wet chemical route. X-ray diffraction pattern confirms the cubic phase of ZnS. TEM images reveal the spherical morphology with the size of 2–5 nm in uniform distribution. Strong blue shift is observed from the UV visible absorption spec- trum with band gap of 4.37 eV. Enhanced photoluminescence near band edge emission is observed at 346 nm. The possible growth mechanism of surface passivation has been discussed. The presence of function- al groups is identified by Fourier transformation infra red spectroscopy and the inorganic elements are iden- tified using energy dispersive X-ray analysis. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Inorganic semiconductors at nanoscale have attracted much inter- est owing to excellent physical, chemical, optical and electrical prop- erties [1–3]. These nano semiconductors are widely used in various fields such as, solar cells, IR detectors, gas sensors [4–6]. Addition of the organic compounds to inorganic semiconductors promises the process ability and flexibility. In particular, the metal chalcogenides coordinating with the organic material show the different surface morphology and size confinement behavior [7,8]. Semiconducting materials can be synthesized by different techniques such as sol gel, wet chemical route, chemical vapor deposition, microwave irradia- tion, sonochemical etc. [9,10]. ZnS (Zinc sulfide) is an important II–VI semiconductor with a wide bandgap energy of 3.68 eV for cubic zinc blende structure and 3.9 eV for wurtzite structure at room temperature [11]. It has been highly at- tractive for its many important technological applications including electroluminescent devices, flat panel displays, infrared windows, sen- sors, lasers, quantum devices etc. [12]. Surface morphology and size con- finement of the nanosemiconductors are important factors for the determination of optical properties [13]. Tuned optical properties of the semiconductors are of current interest in research due to the associ- ation of bandgap with size. Size confinement of semiconductor nanopar- ticles less than those of bulk excitonic Bohr radius result in blue shift in the optical transition and they show high yield photoluminescence properties [14]. These nanoparticles are very promising materials for fluorescent biological imaging and biofunctionalization. In most of the previous reports, the nanoparticles were normally capped with an or- ganic layer such as trioctylphosphine oxide [15], thioglycerol [16] etc. Amines [17] and aniline [18] derivatives can be used as capping agents due to its affinity of the nitrogen atom to the metal ions. In this work, ZnS quantum dots (QDs) were prepared by using N- Methylaniline as a capping agent by wet chemical route. N-Methylaniline capped ZnS QDs were characterized using X-ray powder diffraction (XRD), Transmission electron microscope (TEM), Ultra violet (UV), Photoluminescence (PL), Fourier transform infrared reflectance (FTIR) and Energy dispersive X-ray (EDAX) analysis. 2. Experimental work All the chemicals were of analytical grade. Synthesis of ZnS nanopar- ticles as follows: 50 ml of 0.5 M Zn salt solution was made by dissolving anhydrous Zinc acetate in ethanol and 50 ml of 0.5 M thioacetamide solution was prepared by dissolving thioacetamide in ethanol. Zn salt solution and thioacetamide solution were mixed and stirred at a con- stant rate, to which 0.2 M N-Methylaniline was added. This resulted in a milky white solution, indicating the formation of ZnS. The solution was stirred continuously for 15 h. Subsequently, the resulting milky white solid products were centrifugalized, washed using ethanol and finally dried in vacuum. XRD patterns were recorded using X'per PRO (PANalytical) Dif- fractometer with a monochromatised CuKα (λ = 1.5406 ) radiation in 2θ ranging between 20° and 80° at the scanning rate of 0.017° per 20.67 s. TEM photographs were recorded using JEM 3010 (JEOL) working at 200 kV accelerating voltage. Optical absorption measurement was performed using Varian Cary 5E UV–vis-NIR spectrophotometer in range of 200–800 nm. PL spectrum was obtained by using Fluorolog-3- Materials Letters 68 (2012) 78–81 ⁎ Corresponding author at: Department of Physics, SRM University, Kattankulathur, 603 203, Kancheepuram (D.t), Tamil Nadu, India. Tel.: +91 44 27452818; fax: +91 44 27456255. E-mail address: suruponnus@gmail.com (S. Ponnusamy). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.10.053 Contents lists available at SciVerse ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/matlet