Morphological variations in cadmium sulfide nanocrystals without phase transformation
© Dhage et al; licensee Springer. 2011
Received: 22 December 2010
Accepted: 14 June 2011
Published: 14 June 2011
A very novel phenomenon of morphological variations of cadmium sulfide (CdS) nanorods under the transmission electron microscopy (TEM) beam was observed without structural phase transformation. Environmentally stable and highly crystalline CdS nanorods have been obtained via a chemical bath method. The energy of the TEM beam is believed to have a significant influence on CdS nanorods and may melt and transform them into smaller nanowires. Morphological variations without structural phase transformation are confirmed by recording selected area electron diffraction at various stages. The prepared CdS nanorods have been characterized by X-ray powder diffraction, TEM, UV-Vis spectroscopy, and photoluminescence spectroscopy. The importance of this phenomenon is vital for the potential application for CdS such as smart materials.
Intensive research has been conducted on one-dimensional semiconductors due to their fundamental significance for studying the dependence of various physical properties on dimensionality and size reduction, as well as the potential for applications in nanodevices [1, 2]. In recent years, controlling the morphology and size of nanomaterials has been a crucial issue in nanoscience research due to their fundamental shape- and size-dependent properties and significant applications. Cadmium sulfide (CdS) is one of the important direct band II-VI semiconductors. It has a band gap of 2.4 eV at room temperature, having vital optoelectronic applications for laser light-emitting diodes, and optical devices based on nonlinear properties [3, 4]. As an important II-VI semiconductor material, CdS nanocrystal has received considerable interest from researchers in control of its morphology and size.
The morphology of nanomaterials is a key factor that affects their properties. Nanostructures with novel morphologies have been considerably investigated. There are all kinds of highly faceted geometries such as rods, tetrapods, hexagons, cubes, and pyramids that have been obtained through sequential experiments within the cadmium selenide [5–8]. At the same time, theoretical discussion on the shape-property relation predicted that shape anisotropy induced optical polarization and single-particle electronic state differences. This would generate newer applications for the material and, in turn, stimulate chemists to pursue nanocrystals with novel shapes [9–11]. In recent years, the morphology effect of semiconductor nanocrystallites on their physical properties has aroused extensive attention [12, 13]. Since many fundamental properties of semiconductor materials have been expressed as a function of size and shape, controlling these aspects of semiconductor nanocrystallites would provide opportunities for tailoring properties of materials and offer possibilities for observing interesting and useful physical phenomena. Development of synthetic strategies for CdS nanocrystals of various shapes is still very significant to the field of materials science. The influence of various reaction parameters and solvents on the morphology of CdS nanostructures have been studied extensively by various researchers [14–17].
In this paper, we are reporting on a preparation of CdS nanorods and its novel morphological variation under the TEM beam. This report is the first of its kind to identify such morphological variations of CdS nanorods under a TEM beam. The morphological variations without phase transformations are supported by TEM images and corresponding selected area electron diffraction (SAED) patterns recorded at different stages. They are also supported by the characterization of CdS nanorods by X-ray powder diffraction (XRD), UV-Vis spectroscopy, and photoluminescence (PL) spectroscopy. The importance of this unique phenomenon in CdS nanorods is that it could potentially be applicable for smart materials.
All the chemicals utilized were of AR grade without any further purification (from Sigma-Aldrich). The synthetic method for CdS nanorods used in this work has been based on a previously reported chemical bath technique . The 0.16 M CdSO4 solution was first added to 7.5 M NH4OH solution under constant stirring. Following this, 0.6 M thiourea solution was slowly added to the mixture with rigorous stirring. The bath temperature and pH were maintained at about 65°C and 10, respectively. A precipitated yellow solid product was centrifuged and dried in the oven at 65°C for 4 h.
The crystal phase analysis of the synthesized nanorods was determined by XRD (Cu Kα radiation, X'pert, Philips) with a Bragg angle ranging from 20° to 80°. We then use a TEM (JEOL 100CX, JEOL) with a beam current of 80 μA at an accelerating voltage of 100 kV), to SAED patterns. These were obtained to examine the morphological variations and diffraction patterns at different stages. A TEM sample was then prepared by putting a minute amount of CdS nanorods powder on a carbon-coated copper grid, without dispersing powder in the solvent. The optical absorption of the CdS nanoparticles was then examined by a Perkin-Elmer lambda 20 UV/Visible spectrometer. Lastly, the photoluminescence spectrum was analyzed by a PTI fluorescence spectrometer.
Results and discussions
The formation mechanism of CdS nanorods of cubic Zn-blend structure is due to the aqueous medium and the coordination of thiourea ligand as a molecular template mechanism, wherein temperature and pH are critical conditions. Similarly, Li et al  report the spherical morphology of CdS with cubic Zn-blend structure prepared in water and pyridine at 120°C. More research is being done towards the understanding of nanorod formation and its transformation into small nanowires after melting under a TEM beam.
The CdS nanorods of Zn-blend cubic crystal structure were prepared by a chemical bath method. We demonstrated the transformation of CdS nanorods to small nanowires under a TEM beam without a crystal phase transition. The morphological transformation of CdS nanorods into nanowires without phase transition is a novel and unique phenomenon observed in this specific material. This could be potentially applicable for smart materials, and various other applications can be explored.
We are thankful to the NSF IGERT Materials Creation Training Program (MCTP)-DGE-0654431 for the use of its analytical facilities.
- Xia Y, Yang P, Sun Y, Wu Y, Mayers B, Gates B, Yin Y, Kim F, Yan H: One-Dimensional Nanostructures: Synthesis, Characterization, and Applications. Adv Mater 2003, 15: 353. 10.1002/adma.200390087View ArticleGoogle Scholar
- Tessler N, Medvedev V, Kazes M, Kan S, Banin U: Efficient Near-Infrared Polymer Nanocrystal Light-Emitting Diodes. Science 2002, 295: 1506. 10.1126/science.1068153View ArticleGoogle Scholar
- Gao T, Li QH, Wang TH: CdS nanobelts as photoconductors. Appl Phys Lett 2005, 86: 173105. 10.1063/1.1915514View ArticleGoogle Scholar
- Zhai T, Fang X, Bando Y, Dierre B, Liu B, Zeng H, Xu X, Huang Y, Yuan X, Sekiguchi T, Golberg D: Characterization, Cathodoluminescence, and Field-Emission Properties of Morphology-Tunable CdS Micro/Nanostructures. Adv Funct Mater 2009, 19: 2423. 10.1002/adfm.200900295View ArticleGoogle Scholar
- Peng ZA, Peng X: Mechanisms of the Shape Evolution of CdSe Nanocrystals. J Am Chem Soc 2001, 123: 1389. 10.1021/ja0027766View ArticleGoogle Scholar
- Choi SH, Kim EG, Hyeon TG: One-Pot Synthesis of Copper-Indium Sulfide Nanocrystal Heterostructures with Acorn, Bottle, and Larva Shapes. J Am Chem Soc 2006, 128: 2520. 10.1021/ja0577342View ArticleGoogle Scholar
- Pinna N, Weiss K, Sack-Kongehl H, Vogel W, Urban J, Pileni MP: Triangular CdS Nanocrystals: Synthesis, Characterization, and Stability. Langmuir 2001, 17: 7982. 10.1021/la010287tView ArticleGoogle Scholar
- Warner JH, Tilley RD: Synthesis and Self-Assembly of Triangular and Hexagonal CdS Nanocrystals. Adv Mater 2005, 17: 2997. 10.1002/adma.200501016View ArticleGoogle Scholar
- Fonoberov VA, Pokatilov EP: Exciton states and optical transitions in colloidal CdS quantum dots: Shape and dielectric mismatch effects. Phys Rev B 2002, 66: 85310.View ArticleGoogle Scholar
- Diaz JG, Planelles J: Theoretical Characterization of Triangular CdS Nanocrystals: A Tight-Binding Approach. Langmuir 2004, 20: 11278. 10.1021/la048353pView ArticleGoogle Scholar
- Fonoberv VA, Pokatilov EP, Fomin VM, Devreese JT: Photoluminescence of Tetrahedral Quantum-Dot Quantum Wells. Phys Rev Lett 2004, 92: 127402.View ArticleGoogle Scholar
- Mann S, Ozin GA: Synthesis of inorganic materials with complex form. Nature 1996, 382: 313. 10.1038/382313a0View ArticleGoogle Scholar
- Yang JP, Meldrum FC, Fendler JH: Epitaxial Growth of Size-Quantized Cadmium Sulfide Crystals Under Afrachidic Acid Monolayers. J Phys Chem 1995, 99: 5500. 10.1021/j100015a037View ArticleGoogle Scholar
- Xiong S, Xi B, Qian Y: CdS Hierarchical Nanostructures with Tunable Morphologies: Preparation and Photocatalytic Properties. J Phys Chem C 2010, 114: 14029. 10.1021/jp1049588View ArticleGoogle Scholar
- Yao WT, Yu SH, Liu SJ, Chen JP, Liu XM, Li FQ: Architectural Control Syntheses of CdS and CdSe Nanoflowers, Branched Nanowires, and Nanotrees via a Solvothermal Approach in a Mixed Solution and Their Photocatalytic Property. J Phys Chem B 2006, 110: 11704. 10.1021/jp060164nView ArticleGoogle Scholar
- Cao BL, Jiang Y, Wang C, Wang WH, Wang LZ, Niu M, Zhang WJ, Li YQ, Lee ST: Synthesis and Lasing Properties of Highly Ordered CdS Nanowire Arrays. Adv Funct Mater 2007, 17: 1501. 10.1002/adfm.200601179View ArticleGoogle Scholar
- Hsu YJ, Lu SY: Dopant-Induced Formation of Branched CdS Nanocrystals. Small 2008, 4: 951. 10.1002/smll.200700787View ArticleGoogle Scholar
- Dofia JM, Herrero J: Chemical Bath Deposition of CdS Thin Films: An Approach to the Chemical Mechanism Through Study of the Film Microstructure. J Electrochem Soc 1997, 144: 4081. 10.1149/1.1838140View ArticleGoogle Scholar
- Mahanty S, Basak D, Rueda F, Leon M: Optical properties of chemical bath deposited CdS thin films. J Electron Mater J Electron Mater 1991, 28: 559.View ArticleGoogle Scholar
- Zelaya-Angel O, Alvarado-Gil JJ, Lozada-Morales R, Varges H, Ferreira da Silva A: Band-gap shift in CdS semiconductor by photoacoustic spectroscopy: Evidence of a cubic to hexagonal lattice transition. Appl Phys Lett 1994, 64: 291. 10.1063/1.111184View ArticleGoogle Scholar
- Zhang H, Yang D, Ma X, Ji Y, Li S, Que D: Self-assembly of CdS: from nanoparticles to nanorods and arrayed nanorod bundles. Mater Chem Phys 2005, 93: 65. 10.1016/j.matchemphys.2005.02.011View ArticleGoogle Scholar
- Mayoral A, Anderson PA: Production of bimetallic nanowires through electron beam irradiation of copper- and silver-containing zeolite A. Nanotechnology 2007, 18: 165708. 10.1088/0957-4484/18/16/165708View ArticleGoogle Scholar
- Singh M, Vijay YK, Sharma BK: A variable electron beam and its irradiation effect on optical and electrical properties of CdS thin films. Pramana J Phys 2007, 69: 631. 10.1007/s12043-007-0161-yView ArticleGoogle Scholar
- Spanhel L, Anderson MA: Synthesis of porous quantum-size cadmium sulfide membranes: photoluminescence phase shift and demodulation measurements. J Am Chem Soc 1990, 112: 2278. 10.1021/ja00162a031View ArticleGoogle Scholar
- Li Y, Liao H, Ding Y, Fan Y, Zhang Y, Qian Y: Solvothermal Elemental Direct Reaction to CdE (E = S, Se, Te) Semiconductor Nanorod. Inorg Chem 1999, 38: 1382. 10.1021/ic980878fView ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.