Novel low temperature synthesis and optical properties of 1d znte nanowires

Journal of Science: Advanced Materials and Devices (2018) 226e229 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Novel low-temperature synthesis and optical properties of 1D-ZnTe nanowires Muhammad Arshad Kamran Department of Physics, College of Science, Majmaah University, Majmaah 11952, Saudi Arabia a r t i c l e i n f o a b s t r a c t Article history: Received March 2018 Received in revised form 22 March 2018 Accepted April 2018 Available online April 2018 Low-temperature synthesis of ZnTe nanowires (NWs) is a helpful advancement in realization of low cost nanostructured electronic devices This article reports a novel and low temperature (275  C) synthesis of one-dimensional (1D) NWs of ZnTe on glass substrate X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX) revealed that prepared NWs have good crystallinity and yield Optical properties, reported in this article as UV spectroscopy and photoluminescence (PL), confirm its energy gap of 2.24 eV © 2018 The Author Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: ZnTe Synthesis Low-temperature Optical properties Introduction One dimension (1D) nanostructures have a very important role in nanostructured electronics and application [1] Some applications of 1D nanowires (NWs), nanobelts (NBs), nanoribbons (NRs), and nanotubes (NTs) are nano-electronics, nanophotonics, quantum devices, energy conversion, energy storage, functional nanostructure materials, novel probe microscopy tips, chemical and biological sensing, and nano-bio interfaces [2,3] Among these nanostructures, 1D IIeVI semiconductor nanostructures have been intensively studied due to their attractive electronic and optical properties, which make them potentially ideal building blocks for fabrication of various nanoscale devices including light-emitting diodes (LEDs), solar cells, photodetectors, and diluted magnetic semiconductors (DMS) Among IIeVI semiconductors, ZnTe with a wide and direct band gap of ~2.26 eV, is expected to have useful applications in optoelectronic and thermoelectric devices such as the first unit in a tandem solar cell, green LEDs, a buffer layer for an HgCdTe infrared detector, or a part of the graded p-Zn(Te)Se multiquantum-well structures in a blue-green laser diode, and DMS for spintronic applications [4e6] E-mail address: m.kamran@mu.edu.sa Peer review under responsibility of Vietnam National University, Hanoi There are several synthesis methods employed to grow the ZnTe NWs These are metal-organic chemical vapor deposition (MOCVD) [7], molecular beam epitaxy (MBE) [8,9], electrochemical deposition [10e12], solvothermal [13,14], hydrothermal [15,16], sonochemical [11,17], interfacial synthetic strategy [18], and CVD [19e22] However, some techniques are very expensive like MOCVD, MBE; some need very high temperature (500e1100  C) and/or high vacuum ambient to synthesize 1D nanostructures Though some techniques synthesize 1D ZnTe nanostructures at low temperature like solvothermal, hydrothermal, sonochemical, interfacial synthetic strategy but they produce a lot of defects in the crystals which affect its electronic properties One of the major drawbacks of the above techniques is that there is no control over the diameter of the NWs Recent studies pointed out that the length and diameter of the NWs significantly affect their optical and electrical properties Hence, it is very important to grow NWs with controlled dimensions and at low temperature in order to reduce energy consumption in manufacturing process which as a result decreases the production cost In this article, we report the ZnTe NWs prepared by lowtemperature vapor-liquid-solid (VLS) growth without using any kind of carrier gas This method has several advantages over other usual methods like energy-saving and cost-effective approach, and it does not require any sophisticated procedure and equipment This novel synthesis method provides an easy way to develop the nanostructures and related devices https://doi.org/10.1016/j.jsamd.2018.04.001 2468-2179/© 2018 The Author Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/) M.A Kamran / Journal of Science: Advanced Materials and Devices (2018) 226e229 227 Experimental ZnTe NWs (111) 2.1 Growth of ZnTe nanowires 2.2 Materials characterization The structural analysis was performed by using X-ray diffractometer (Burker, D8 Advance) operating CuKa at 40 kV and 40 mA to generate wavelength 1.54056 Å and engaging scanning rate of 0.02 deg/s in 2q range from 20 to 60 The morphology and chemical compositional analysis of the ZnTe NWs were characterized by field emission scanning electron microscope (FEI, FESEM Quanta-450) equipped with an air cooled energy dispersive x-ray spectrometer (Thermo Ultra dry EDX) UVevisible absorption spectra of the samples were carried out by double beam spectrometer (Jesco V-570) Photoluminescence spectrum were recorded at room temperature by DWoptron spectrometer equipped with lock-in amplifier (Stanford SR510) based deduction system 4.8 (331) Counts × 103 3.2 1.6 (222) (200) 1D nanowires of ZnTe were synthesized by low-temperature VLS method In the preparation a 50 mg of ZnTe powder (Alfa Acer; 99.995%) was dissolved in 25 ml methanol Firstly, we used high powered Digital Sonifier (Branson Model 450) to dissolve it in methanol for 15 and then kept it in the covered beaker for 24 h Then again give sonication for 15 before spin-coat at 4000 rpm on glass substrates Cleaned and dried glass substrates cut in size of  cm2 from microscopic glass slides were used for the deposition of ZnTe NWs To make a thicker film, these procedures were repeated ten times with the gap of in each spin coat deposition A nm thin film of gold as catalyst was deposit by sputter coater on the top of spin coated films A special designed glass enclosure was used that closed from all sides and caped just above the 100 mm over the substrate containing the spin-coated ZnTe film A computer controlled programmable Nabertherm furnace was used to synthesis ZnTe NWs A three stage ramped temperature was programed to steadily reached the celling temperature 275  C and kept constant for h Resultant product was allowed to remain inside furnace till it reached ambient temperature (220) 6.4 0.0 20 30 40 50 60 Theeta (degree) Fig XRD pattern of ZnTe NWs as grown on glass substrate and then grow NWs at high temperature i.e 800e9500  C) and used very expensive sapphire substrates [2] 3.3 Composition analysis An EDX spectrum of as-grown ZnTe NWs is illustrated in Fig shows that the NWs are only composed of Zn and Te Their composition is listed in Table A comparatively every small peak of Si having only 0.72% is coming from the glass substrate It confirms the high purity of ZnTe NWs Results and discussion 3.1 Crystal structure analysis The phase structure of the as-synthesized product was analyzed by X-ray diffraction (XRD) The XRD pattern of ZnTe NWs is shown in Fig The diffraction peaks are at 2q values of 25.239, 29.189, 41.789, 49.489, 51.841 and 60.639 were identified and indexed to originate from (111), (200), (220), (311), (222) and (400) crystal planes It can be attributed to cubic ZnTe crystal with lattice constant 6.11 Å and having the space group F-43m which is in good agreement with the standard JCPDS (Card No 00-015-0746) 3.2 Morphology Fig 2(a) shows the low magnification FESEM image of ZnTe NWs deposited on the glass substrate It can be seen that the substrate is fully covered with smooth and very long NWs showing high aspect ratio There was no region on  cm2 glass substrate which shows un-complete growth as observed by Li Jin at el [23] Fig 2(b) is the magnified FESEM image of an individual ZnTe NW By close examination, it can be seen that the NW has uniform diameter of approximately 60.23 nm (Fig 2(b)) These NWs were grown at very low temperature, i.e 275  C and have much better quality as compared to NWs prepared by a complex growth method (first annealed sapphires at 1400e1600  C, then patterning at 550  C, Fig FESEM images of ZnTe NWs as grown on glass substrate (a) at low magnification (b) a lift of NW at higher magnification 228 M.A Kamran / Journal of Science: Advanced Materials and Devices (2018) 226e229 Fig EDX spectrum of ZnTe NWs Table A compositional EDX analysis of ZnTe NWs Fig PL spectrum of ZnTe NWs taken on the excitation laser wavelength of 325 nm Element line Element Wt.% Atom % Compound Wt.% Zn L Te L 21.04 78.24 33.51 63.83 21.04 78.24 the direct band gap This intercept is required band of ZnTe have Eg ¼ 2.24 eV, which is very closely matched with the previous finding [24,25] 3.4 UVevisible absorption spectroscopy 3.5 Photoluminescence (PL) studies The optical absorption spectrum of ZnTe NWs was measured by double beam spectrometer (Jesco V-570) Analysis of absorbance spectrum with the help of Tauc's law is plotted for the calculation of energy bandgap (Eg) and the nature of the transition is shown in Fig For exploring the optical behavior of ZnTe NWs, PL spectrum of the product was measured at room temperature A continuous wave (cw) laser of wavelength 325 nm is used to excite ZnTe NWs Fig shows the PL emission spectrum of as-grown ZnTe NWs The PL emission measured in the range of 460e800 nm has shown only narrow emission centered at 551 nm The luminescence at 551 nm endorsed red emission from the ZnTe NWs A single PL peak originates from the band-edge (BE) transitions of ZnTe NWs Absence of broad emission peak in the range 600e750 nm associated with the oxygen doping, Te vacancies, Zn-Te composite vacancies (VZn-Te) validate that as-synthesized ZnTe NWs possess high quality optical properties [26] À ahv ¼ A hv À Eg Án (1) where A is a constant (slope), Eg is the optical bandgap and n depends upon the nature of transition (n ¼ 1/2 referred as indirect bandgap as per Davis-Mott model and n ¼ referred as direct bandgap as per Tauc's model) Fig displays the Tauc's plot exhibiting (ahn)2 versus hv for calculation of direct band gap The direct bandgap was found by extrapolating (ahn)2 versus hv graph on the horizontal axis at a ¼ Our results show that ZnTe NWs has Conclusion The simple and low temperature (275  C) synthesis method for preparation of ZnTe NWs has been described The XRD pattern of ZnTe NWs shows the prepared NWs are single crystalline (cubic phase), having the lattice constant of 6.11 Å The FESEM and EDX results authenticate that the NWs have a very large aspect ratio and their composition without any other phases Absorbance, PL spectrum, and calculation of bandgap from both results are in good agreement with the energy gap measured for the ZnTe in the cubic phase Hopefully this synthesis method may play a commendable role for the cost effect production of ZnTe nanostructures, especially NWs and nanodevices Acknowledgements “This Article contains the results and findings of a research project that is funded by King Abdul Aziz City for Science and Technology (KACST) Grant No LGP-36-173” Author is also thankful for the technical and academic support and discussion with Prof Abdul Majid of Physics at Majmaah University, Saudi Arabia, for the preparation of this article and research work References Fig UVevis analysis for the measurement of band gap by using Tauc law The inset shows the absorbance plot of the ZnTe NWs [1] M Law, J Goldberger, P.D Yang, Semiconductor nanowires and nanotubes, Annu Rev Mater Res 34 (2004) 83e122 M.A Kamran / Journal of Science: Advanced Materials and Devices (2018) 226e229 [2] G Reut, E Oksenberg, R Popovitz-Biro, K Rechav, E 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NWs, PL spectrum of the product was measured at room temperature A continuous... (2018) 226e229 Fig EDX spectrum of ZnTe NWs Table A compositional EDX analysis of ZnTe NWs Fig PL spectrum of ZnTe NWs taken on the excitation laser wavelength of 325 nm Element line Element Wt.%