This article reports a novel and low temperature 275C synthesis of one-dimensional 1D NWs of ZnTe on glass substrate.. Though some techniques synthesize 1D ZnTe nanostructures at low tem
Trang 1Original 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
Article history:
Received 7 March 2018
Received in revised form
22 March 2018
Accepted 1 April 2018
Available online 6 April 2018
Keywords:
ZnTe
Synthesis
Low-temperature
Optical properties
a b s t r a c t
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 (275C) synthesis of one-dimensional (1D) NWs of ZnTe on glass substrate X-ray diffraction (XRD), scanning electron mi-croscopy (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 photo-luminescence (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/)
1 Introduction
One dimension (1D) nanostructures have a very important
role in nanostructured electronics and application [1] Some
applications of 1D nanowires (NWs), nanobelts (NBs),
ribbons (NRs), and nanotubes (NTs) are electronics,
nano-photonics, 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
nano-structures 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,
photodetec-tors, 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
optoelec-tronic 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
multi-quantum-well structures in a blue-green laser diode, and DMS
for spintronic applications[4e6]
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 deposi-tion [10e12], solvothermal [13,14], hydrothermal [15,16], sono-chemical [11,17], interfacial synthetic strategy [18], and CVD [19e22] However, some techniques are very expensive like MOCVD, MBE; some need very high temperature (500e1100C)
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 low-temperature 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
E-mail address: m.kamran@mu.edu.sa
Peer review under responsibility of Vietnam National University, Hanoi.
Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d
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://
Trang 22 Experimental
2.1 Growth of ZnTe nanowires
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 min and then kept it in the covered beaker for 24 h
Then again give sonication for 15 min before spin-coat at 4000 rpm
on glass substrates Cleaned and dried glass substrates cut in size of
1 1 cm2from microscopic glass slides were used for the deposition
of ZnTe NWs To make a thickerfilm, these procedures were repeated
ten times with the gap of 1 min in each spin coat deposition A 5 nm
thinfilm of gold as catalyst was deposit bysputter coateron the top of
spin coatedfilms A special designed glass enclosure was used that
closed from all sides and caped just above the 100mm over the
substrate containing the spin-coated ZnTe film A computer
controlled programmable Nabertherm furnace was used to
syn-thesis ZnTe NWs A three stage ramped temperature was programed
to steadily reached the celling temperature 275C and kept constant
for 2 h Resultant product was allowed to remain inside furnace till it
reached ambient temperature
2.2 Materials characterization
The structural analysis was performed by using X-ray
diffrac-tometer (Burker, D8 Advance) operating CuKaat 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
character-ized byfield 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
spec-trometer (Jesco V-570) Photoluminescence spectrum were
recor-ded at room temperature by DWoptron spectrometer equipped
with lock-in amplifier (Stanford SR510) based deduction system
3 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
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
con-stant 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
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 1 1 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 1400e1600C, then patterning at 550C,
and then grow NWs at high temperature i.e 800e9500C) and
used very expensive sapphire substrates[2] 3.3 Composition analysis
An EDX spectrum of as-grown ZnTe NWs is illustrated inFig 3 shows that the NWs are only composed of Zn and Te Their composition is listed inTable 1 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
0.0 1.6 3.2 4.8 6.4
ZnTe NWs
2 Theeta (degree)
Fig 1 XRD pattern of ZnTe NWs as grown on glass substrate.
Fig 2 FESEM images of ZnTe NWs as grown on glass substrate (a) at low magnifica-tion (b) a lift of NW at higher magnificamagnifica-tion.
Trang 33.4 UVevisible absorption spectroscopy
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
(1) where A is a constant (slope), Egis the optical bandgap and n
de-pends upon the nature of transition (n¼ 1/2 referred as indirect
bandgap as per Davis-Mott model and n ¼ 2 referred as direct
bandgap as per Tauc's model) Fig 4 displays the Tauc's plot
exhibiting (ahn)2versus hv for calculation of direct band gap The
direct bandgap was found by extrapolating (ahn)2versus hv graph
on the horizontal axis ata¼ 0 Our results show that ZnTe NWs has
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]
3.5 Photoluminescence (PL) studies 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
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 orig-inates 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]
4 Conclusion The simple and low temperature (275C) 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 spec-trum, 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
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Table 1
A compositional EDX analysis of ZnTe NWs.
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Fig 4 UVevis analysis for the measurement of band gap by using Tauc law The inset
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