Journal of Nanomaterials & Molecular NanotechnologyISSN: 2324-8777

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Research Article, J Nanomater Mol Nanotechnol Vol: 6 Issue: 2

Interconnections between Ag- NWs Build by Argon Ions Beam Irradiation

Honey S1,3,4,*, Naseem S1, Ishaq A2,3,4, Maaza M3,4, Bhatti MT5 and Madhuku M6
1Centre of Excellence in Solid State Physics, University of Punjab, QAC, Lahore, Pakistan
2National Center for Physics, Quaid-i-Azam University, Islamabad 44000, Pakistan
3UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk ridge, P.O. Box 392, Pretoria-South Africa
4Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure road, Somerset West 7129, P.O. Box 722, Somerset West, Western Cape Province, South Africa
5Department of Physics, Bahauddin Zakariya University, Multan 60800, Pakistan
6iThemba LABS, National Research Foundation, P. Bag X11, WITS 2050, South Africa
Corresponding author : Honey Shehla
Centre of Excellence in Solid State Physics, University of Punjab, QAC, Lahore, Pakistan; UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology, College of Graduate Studies, University of South Africa
Muckleneuk ridge, P.O. Box 392, Pretoria-South Africa; Nanosciences African Network (NANOAFNET), iThemba LABSNational Research Foundation, 1 Old Faure road, Somerset West 7129, P.O. Box 722, Somerset West, Western Cape Province, South Africa E-mail: [email protected]
Received: June 21, 2016 Accepted: December 31, 2016 Published: January 06, 2017
Citation: Honey S, Naseem S, Ishaq A, Maaza M, Bhatti MT, et al. (2017) Interconnections between Ag-NWs Build by Argon Ions Beam Irradiation. J Nanomater Mol Nanotechnol 6:2. doi: 10.4172/2324-8777.1000213

Abstract

Interconnections between Ag- NWs Build by Argon Ions Beam Irradiation

Interconnection between Ag-NWs is essential for the integration and assembly of NWs networks to enable optoelectronics and nanoelectronics applications. In this report, joining of Ag-NWs through argon ion beam irradiation technology is demonstrated. A range of experimental traits of constructing X-, and II-shapes molecular junctions between Ag nanowires and the utilization of the argon ion beam irradiation induced nanowelding technique to form functional metal NWs networks is conferred. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy results revealed that Ag-NWs are effectively connected to each other on intersecting positions. These networks are optically transparent and crystal structure remained un-damaged. Besides, technical hindrances facing the ion irradiation induced nanowelding technology are also discussed. A perspective is given for using argon ion irradiation induced welding technique for the construction of random networks of well-connected nanowires.

Keywords: Ag-NWs; Argon ions; Irradiation; Interconnection; X-shape; IIshape; XRD; Optical

Keywords

Ag-NWs; Argon ions; Irradiation; Interconnection; X-shape; IIshape; XRD; Optical

Introduction

Owing to their unique physical properties and availability in various types of structures, metal nanowires such as silver nanowires have potential applications in functional nano devices such as optoelectronic devices, electronic devices, and sensors [1-3].
Moreover, the nano devices can also be interconnected to each other using metal nanowires [2]. For device integration of these nanowires, effective interconnection between nanowires is essential. Various nano-fabrication techniques have been introduced for joining of these nanowires; however, nanowires can be interconnected almost perfectly through various welding technique [2]. Nano welding is bottom-up nano fabrication technique through which nanowires can be assembled directly together in form of functional networks [2].
There are several nano welding techniques including joule heat welding [4,5], electron beam heating [6], self-limited plasmonic welding [7], nanoscale soldering [8], electron beam welding [9], cold welding [7], ultrasonic welding [10] etc. All of these techniques have several downsides and some benefits as well. However, to achieve perfect interconnection is a major technical resist for all of these techniques. Besides above mention techniques, ion beam irradiation is another approach to interconnect these nanowires in the form of functional complex networks in a controlled manner. Moreover, the interconnections on a large-scale can be easily realized by the present argon ion beam irradiation technique. Herein, we report interconnection between Ag-NWs on intersecting positions by argon beam irradiation. Interconnection in various shapes between Ag- NWs is achieved and discussed here.

Experimental Details

The Ag-NWs were purchased from American Chemical Society (ACS) materials having diameter varying in the range 100-200 nm. These Ag-NWs have average length of 20 μm. Initially, these Ag- NWs were dispersed in iso-propanol with concentration 25 mg/ ml. this solution was diluted down to 0.5 mg/ml. The solution was dropped on copper grid and on glass substrate. Thereafter, those samples were exposed to 3.5 MeV Ar ions beam at fluence 5×1016 ions/cm2 in 5UDH-Pelletron accelerator. Ar ion beam irradiation current, substrate temperature and exposure time were 0.1 μA, room temperature and one hour respectively. SRIM simulation was done to make it certain that Ar ions are not implanting into nanowires [11]. Before and after Ar beam irradiation, the samples were characterized for their and morphology using SEM, TEM and XRD. These samples were characterized optically using UV-VIS spectroscopy.

Results and Discussions

Figure 1 represents TEM images of Ag-NWs networks before and after argon ions irradiation. It is found in Figure 1(a) that these NWs are not connected to each other before irradiation. After exposing to argon beam of energy 3.5 MeV and of fluence 5×1016 ions/cm2, the interconnection is obvious and can be seen in Figure 1(b). It depicts the joining of NWs after argon irradiation.
Figure 1: (a) TEM image of silver NWs (a)before irradiation (b) after irradiation with 3.5 MeV Ar ions beam and with a fluence of 5×1016 ions/cm2 (c) II junction (d) X junction.
Moreover, scanning electron microscopy is performed for verification of TEM results. Before and after exposing to argon ions at a fluence of 5×1016 ions/cm2, SEM images are given in Figure 2(a) and 2(b). The SEM images at higher magnification of interconnected Ag-NWs exposed at a fluence of 5×1016 ions/cm2 are given in Figure 2(c) and 2(d). It is expected from SEM analysis that nanowires were connected due to melting, fusion and solidification process or due to collection of atoms sputtered from lattices of NWs. In previous report, interconnections between multi-walled carbon nanotubes were achieved by Ar ion beam irradiation [11].
Figure 2: (a) SEM image of silver NWs (a) before irradiation (b) after irradiation with 3.5 MeV Ar ions beam and with a fluence of 5×1016 ions/cm2 (c) X junction (d) II junction.
The individual Ag-NWs are interconnected to each other might be because of heat induced due to high energy Ar ions beam or due to continual ejection of atoms from NWs lattices. The interaction of ions with NWs lattices may be of two type’s i-columbic interaction with electrons in the atoms or ii-elastic collision with nuclei of atom. If the interaction is elastic, it will lead to continual atomic ejection from the lattices of NWs. An individual ejected atom will strike with another atom and cause to produce a series of atomic ejections before coming to rest. The sputtered silver atoms and disordered lattices are enough to result in the interconnection of the two adjacent NWs. Therefore the nanowires may interconnect to each other due to agglomeration of argon irradiation-induced sputtered silver atoms from individual silver NWs.
In case, if interaction is columbic, the heat would be generated, lead to diffuse the atoms and finally heat would be dissipated [12-14]. Usually, metals would absorb all the heat energy that appeared due to ionization and consequently the temperature is raised to such an extent that is sufficient to melt the NWs. NWs in melted form may connect to each other in better way at intersecting points. Once the NWs are melted, thermal conduction is initiated within NWs, and finally the generation and conduction of heat is ceased. The heat is lost due to convection from the surfaces, the temperature falls down rapidly at intersection points and finally metal solidified and nanowires are welded. Due to convection from the NWs surface, the heat is lost and causes to fall down the temperature at intersection points, metal cool down and nanowires are interconnected with each other.
In order to verify the above mention phenomena which might accountable to interconnect these Ag-NWs, SRIM (Stopping and Range of Ions in Matter) has been carried out [11]. The parameters for SRIM calculations were i) ion beam energy of 3.5 MeV, ii) 1000 ions iii) incident angle of 0. The graphical representation of ions tracks (depth vs. Y-axis) and events of collisions are shown in Figure 3(a) and 3(b), respectively.
Figure 3: The schematic representation of SRIM simulation for interaction of 3.5 MeV Ar ions with Ag layer (a) (Ions trajectories) depth vs. Y-Axis (b) collision events.
Moreover, simulation calculation results for impact of 3.5 MeV Ar ions with Ag layer are given in Table 1, which represents the total damage created and total loss of energy due to ions and recoils. The term “ionization” indicates the loss of energy to target electrons. The data collected for ions is representing the direct loss of energy of ions in Ag whereas the data collected for recoils is the loss in energy of recoiling Ag atoms due to transfer to target electrons. Therefore, it is confirmed from SRIM simulation results that interaction of Ar ions into Ag target leads to two phenomena i) generation of heat due to ionization ii) production of lattice defects or vacancies. In Figure 3(a), the red dots are indicating the production of vacancies.
Table 1: SRIM simulation results of 3.5 MeV Ar ions in layer of Silver at incident angle 0°.
Structure of un-irradiated and 3.5 MeV Ar irradiated Ag-NWs networks are verified by XRD analysis. The XRD spectra were recorded at room temperature and are seen in Figure 3. It is obvious that XRD pattern exhibits peaks of face centered cubic planes (111) and (200) of Ag-NWs (JCPDS Card No. 04-0783) [15]. No significant changes have been observed in angle positions after Argon irradiation; however, the intensity of peaks is abruptly enhanced after exposure to argon beam. This enhanced intensity of peaks is attributed to improved crystalline structure might possibly due to perfect joining of NWs. Moreover, lattice constant is calculated and found to be 4.081 Å. The lattice constant value is well matched with value found in literature for Ag [16]. This is a clear indication for stability in structure after exposure to argon beam.
The optical properties of Ag-NWs networks arise due to surface plasmonic resonance effect and are variant as compared to bulk silver. The optical absorbance spectra of pristine and Ar irradiated Ag-NWs networks are demonstrated in Figure 4 (a) and 4(b). The spectra revealed strong absorption and lower transmittance band approximately at 332 nm which is in ultraviolet region and might be due to surface plasmonic resonance effect [17,18,19]. While the dimensions of wires is reduced down to nanoscale regime, absorbance band appear in UV region of UV-Vis spectra of Ag-NWs Figure 5. In case of bulk silver, this band is absent in UV region. The reason for appearance of this absorption band is may be the interaction of conduction electron with an electromagnetic field [18,19]. Another observation is reduction in optical absorbance with increase in argon fluence which indicating enhanced transmittance. It might be due to improvement in crystal structure due to optimal joining of nanowires in the network of Ag-NWs.
Figure 4: XRD patterns of Ag-NWs (a) un-irradiated (b) irradiated by Ar ions at a beam fluence of 5×1016 ions/cm2.
Figure 5: Absorbance spectra for Ag-NWs networks (a) un-irradiated (b) Ar irradiated at a beam fluence of ~5×1015 ions/cm2.

Conclusion

Perfect interconnections on overlapping points between Ag-NWs are successfully achieved by exposing to 3.5 MeV argon ions. These nanowires were interconnected might be due to argon irradiated induced melting of Ag-NWs and series of atomic ejections and collections at intersecting sharp angle positions. The structure of Ag-NWs in the networks remained un-damaged during Ar ions irradiation. These networks were found to be optically transparent. It has so far been believed that synthesis of interconnections between metallic nanowires is very important in nanoelectronics and circuit industry. The present argon ions irradiation technology was proved to be a superb approach to achieve perfect interconnection between metallic nanowires. The ion irradiation technology combined provides a possible approach for the construction of NWs interconnection for application in future nanodevices.

Acknowledgements

Authors of this work greatly acknowledge the support of Higher Education Commission (HEC) of Pakistan, iThemba LABS South Africa, TWAS, UNESCO and UNISA.

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