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Anodic-aluminum-oxide template assisted fabrication of cesium iodide (CsI) scintillator nanowires
Materials Letters 112 (2013) 190–193
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Anodic-aluminum-oxide template assisted fabrication of cesium iodide (CsI) scintillator nanowires Chien Chon Chen a, Shao Fu Chang a, Zhiping Luo b,n a
Department of Energy Engineering, National United University, Miaoli 36003, Taiwan Department of Chemistry and Physics and Southeastern North Carolina Regional Microanalytical and Imaging Consortium, Fayetteville State University, Fayetteville, NC 28301, USA
b
art ic l e i nf o
a b s t r a c t
Article history: Received 1 August 2013 Accepted 4 September 2013 Available online 13 September 2013
Real-time digital imaging of radiation is realized using scintillators, and vertically aligned scintillator structures improve the spatial resolution and detection efficiency. In this work, a cost-effective approach was developed to prepare scintillator CsI nanowires in anodic aluminum oxide (AAO) nanochannels by a mechanical injection method. The AAO walls were pre-deposited with CsI nanoparticles using CsI aqueous solution to facilitate complete filling of the nanochannels. It was observed that although CsI solidifies as dendritic structures in free space on the surface of glass slides, when it is injected into the AAO nanochannels, it solidifies as stable single wires. This mechanical injection method enables fabrication of CsI nanowires with controllable size and chemical doping levels. & 2013 Elsevier B.V. All rights reserved.
Keywords: Electron microscopy Fabrication Nanowires Scintillator Solidification
1. Introduction Since the discovery of X-rays by Röntgen in 1895, radiation detection has been a rather long-time research topic that is still under development [1–3]. The traditional method to record the radiation using silver films (radiography) requires chemicals and consumables, which yields high cost and wastes to the environment. Currently the radiography is being replaced with scintillator detectors. The scintillator crystals, when excited by the radiation energy, can generate visible light that can be detected using charge-coupled device, and thereby enabling real-time digital imaging [1–3]. Thallium doped CsI scintillator is one of the brightest scintillators, with maximum wavelength of light emission around 550 nm, well suited for photodiode readout. It has been widely used for detecting X- or γ-rays. To date, the CsI(Tl) scintillators have been prepared in the following ways: (1) Traditional continuous thin foils by various deposition methods from solutions, typically containing plastic scintillator dissolved in toluene or xylene. The thin scintillator foils were obtained by solvent dissolution by flotation of the scintillator solution on water [4,5], evaporating the scintillator solution in vacuum [6], or spinning the scintillator solution on a rotating plate to obtain uniform foils [7,8].
n
Corresponding author. Tel.: þ 1 910 672 2647; fax: þ1 910 672 2420. E-mail address: [email protected] (Z. Luo).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.09.017
(2) Vertically aligned needle or micro-columnar structures [9–12] by various vapor deposition methods. Such vertically grown structures reduce the lateral spreading of light, and therefore improve the detector spatial resolution [12]. (3) Scintillators in silicon microcavities, microchannels or wells with light guides [13–15]. In a report by Rocha and Correia [13], a deep reactive-ion etching technique was used to achieve vertical side-walls with 100 mm pixel squares. However, there are several challenges associated with the current developments of these scintillator detectors, such as high cost to produce the Si microchannels which involve multiple procedures [3], and the channel size is in the order of several micrometers or larger, and there is no report on smaller channels under micrometer. In this work, a new low-cost approach to fabricate scintillator crystals using anodic aluminum oxide (AAO) rather than Si is reported, which can produce scintillator crystals with a wide range of controllable size to optimize their performance in X- or γ-ray detection. 2. Experimental procedure The starting material is high-purity aluminum (Al) substrate (99.999%). At first, the Al substrate was mechanically polished and annealed in an air furnace at 550 1C for 1 h to remove surface stress concentration. The sample was then electro-polished in a bath consisting of 15 vol% perchloric acid (HClO4, 70%), 70 vol% ethanol
C.C. Chen et al. / Materials Letters 112 (2013) 190–193
(C2H6O, 99.5%), and 15 vol% monobutylether ((CH3(CH2)3OCH2CH2OH), 85%) at applied voltage of 42 V (DC) for 10 min, using a platinum plate as a counter. The AAO with larger pores were prepared using 1 vol% H3PO4 þ5 vol% ethylene glycol (C2H4(OH)2) at 195 V and 3 1C, and smaller pores, using 3 wt% C2H2O4, at 40 V and 25 1C. After the first anodization for 40 min, the anodization film was removed in 1.8 wt% chromic acid (CrO3)þ6 vol% H3PO4 solution at 70 1C for 40 min. With regular patterns on the surfaces, the samples were used for the second anodization under the same conditions but for 1–24 h. The longer anodization time resulted deeper AAO channels. They were then widened in 5 vol% H3PO4 at 25 1C for 4 h and 1.5 h to obtain final nanopores with 450 nm and 100 nm in diameter, respectively. The microstructure and composition of the fabricated samples were studied using optical microscopy (Nikon LV 150), scanning
191
electron microscopy (SEM, JEOL 7400 and 6510 LV), X-ray energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD, PHILIPS X′Pert Pro).
3. Results and discussion Fig. 1 schematically depicts the fabrication of CsI nanowires by mechanical injection method using highly ordered AAO (Fig. 1a) as template. At first, CsI nanoparticles were deposited on AAO walls using the dip–dry method. Aqueous solution containing 1 wt% CsI was dropped on the AAO template, which was then placed on a hot plate to dry at 100 1C. It was found that CsI nanoparticles were deposited on the AAO inner walls (Fig. 1b). Since the melting point of CsI is relatively low (621 1C), the mechanical injection method [16–20] can be adopted to fabricate CsI nanowires in AAO. The schematic apparatus can be
Glass CsI Raw Material
Glass CsI Liquid
AAO
AAO/CsI
AAO/CsI
AAO/CsI
AAO/CsI
Barrier layer Al
Barrier layer Al
Barrier layer Al
Barrier layer Al
Barrier layer
Fig. 1. Schematic step-by-step fabrication procedure. (a) AAO; (b) CsI nanoparticles solidified on AAO walls, (c) before injection; (d) after injection; and (e) AAO/CsI.
Fig. 2. CsI nanoparticles (indicated) solidified on AAO walls. (a, b) SEM images; (c) XRD; and (d) EDS.
192
C.C. Chen et al. / Materials Letters 112 (2013) 190–193
found in previous publications [16,19,20]. Inside of the vacuum chamber ( 10 2 Torr) of the mechanical injection device, AAO template with CsI nanoparticles was placed on the bottom side, and raw material of CsI particles are on its top (Fig. 1c). When the device was heated up at 630 1C above the melting temperature of CsI, a hydraulic force ( 10 kgf/cm2) was applied to inject the molten CsI
into the nanopores of the AAO template (Fig. 1d). After the injection process, the chamber was kept in vacuum to cool down slowly. The remaining Al substrate can be removed mechanically, followed with dissolution in an etching solution of 10 wt% CuCl2 and 8 vol% HCl until Al is dissolved, and the solidified CsI layers covering on the top surface of AAO should also be removed mechanically (Fig. 1e).
Fig. 3. Optical images of CsI with dendritic structure solidified from 1 wt% CsI solution (a, b) and melt (c, d).
Fig. 4. SEM images of CsI nanowires. (a) Partially retained CsI on AAO; (b) CsI nanowires in AAO; (c) lateral view; and (d) cross-sectional view of CsI nanowires.
C.C. Chen et al. / Materials Letters 112 (2013) 190–193
The ionic bonds in CsI can be dissolved in a polarized H2O aqueous solution. Fig. 2 shows SEM images of CsI nanoparticles solidified on top (Fig. 2a) and bottom of AAO walls (Fig. 2b), formed by immersing AAO into 1 wt.% CsI solution and dried on a hot plat at 100 1C. The XRD pattern in Fig. 2c shows peaks from both CsI and Al substrate, as well as impurity byproducts of Al2O3 and AlPO4. The EDS spectrum (Fig. 2d) confirms the elements in CsI, as well as Al, O, C and P elements. When Al is anodized in H3PO4 containing aqueous solution, the hydrogen (H þ ) ions are absorbed on the cathode forming hydrogen gas (H2); while on the other electrode, the OH , H2 PO4 , HPO24 , and PO34 ions are absorbed on the anode and reacts with aluminum (Al3 þ ) ion forming phosphor doped aluminum hydroxide Al(OH)3) or boehmite (Al2O3 H2O) films. The film can further transform to alumina film after heat treatment. When 1 wt% CsI solution is dried on the surface of a glass slide, dendritic structures are formed, as shown in Fig. 3(a) and its enlargement in Fig. 3(b). However, when CsI is solidified from the melt (630 1C) to 25 1C on a glass slide in an air furnace, both dendrites and bubble pits are formed, as shown in Fig. 3(c) and a picture showing the pits only is presented in Fig. 3(d). Whether CsI solidifies from the aqueous solution or melt on the glass slides, dendrites can grow in the three-dimensional (3D) free space to form 3D patterns, without any external restrictions to their growth. The pits are associated with the evaporation of the melt during the solidification process. Using the AAO pre-deposited with CsI nanoparticles as template, CsI melt was mechanically injected into the AAO nanochannels to obtain larger (Fig. 4a–c) or smaller (Fig. 4d) nanowires, with diameters of 450 nm and 100 nm, respectively. In Fig. 4(a), partial CsI layer retains on top of AAO, and in Fig. 4(b), AAO is almost completely filled with CsI nanowires. From the lateral view in Fig. 4(c), the larger CsI nanowires almost filled the entire channels over the length. From the fracture of CsI-filled AAO film in Fig. 4(d), highly ordered CsI nanowires are obtained. It should be mentioned that if the CsI nanoparticles were not pre-deposited on AAO, very limited AAO nanochannels could be filled with CsI by mechanical injection. The pre-deposited CsI reduced the contact angle between the CsI melt and AAO. It is interesting that when CsI melt is confined in AAO nanochannels, it grows as stable single wires without any dendrites, consistent with the previous theoretical predictions [21]. 4. Conclusions In summary, highly ordered CsI nanowires, with diameters between 100 and 450 nm, were prepared using cost-effective mechanical injection method. Although various methods were used to fabricate different nanowires in the past [22–24], the mechanical injection method seems to be the most suitable one to fabricate the CsI nanowires which it does not require any chemical
193
precursors. Their size can be controlled by the AAO pores, and Tl doping level, by the composition of starting raw materials.
Acknowledgments This work was financially supported by the Chung-Shan Institute of Science and Technology (CSIST) under the Contract no. CSIST-442-V103. The SEM performed at SENCR-MIC was supported by FSU Faculty Startup Fund. The SENCR-MIC was funded by the U.S. Army Research Office under Contract no. W911NF-09-1-0011.
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2013.09.017. References [1] Gruner SM. Physics Today 2012;65:29–34. [2] Nikl M. Measurement Science and Technology 2006;17:R37–54. [3] Rocha JG, Lanceros-Mendez S. Recent Patents on Electrical Engineering 2011;4:1–26. [4] Yaffe L. Annual Review of Nuclear Science 1962;12:153–88. [5] Muga ML, Burnsed DJ, Steeger WE. Nuclear Instruments and Methods in Physics 1972;104:605–10. [6] Ajitanand NN, Iyengar KN. Nuclear Instruments and Methods in Physics 1976;133:71–4. [7] Norbeck E, Dubbs TP, Sobotka LG. Nuclear Instruments and Methods in Physics Research A 1987;262:546–7. [8] Weathers LW, Tsang MB. Nuclear Instruments and Methods in Physics Research A 1996;381:567–8. [9] Fujieda I, Cho G, Drewery J, Gee T, Jing T, Kaplan SN, et al. IEEE Transactions on Nuclear Science 1991;38:255–62. [10] Jing T, Goodman CA, Drewery J, Cho G, Hong WS, Lee H, et al. IEEE Transactions on Nuclear Science 1994;41:903–9. [11] Nagarkar VV, Gupta TK, Miller SR, Klugerman Y, Squillante MR, Entine G. IEEE Transactions on Nuclear Science 1998;45:492–6. [12] Nagarkar V, Gaysinskiy V. US patent 7696482 B1; 2010. [13] Rocha JG, Correia JH. Sensors and Actuators A 2001;92:203–7. [14] Badel X, Galeckas A, Linnros J, Kleimann P, Fröjdh C, Petersson CS. Nuclear Instruments and Methods in Physics Research A 2002;487:129–35. [15] Rocha JG, Ramos NF, Lanceros-Mendez S, Wolffenbuttel RF, Correia JH. Sensors and Actuators A 2004;110:119–23. [16] Chen CC, Bisrat Y, Luo ZP, Schaak RE, Chao CG, Lagoudas DC. Nanotechnology 2006;17:367–74. [17] Chen SH, Chen CC, Luo ZP, Chao CG. Materials Letters 2009;63:1165–8. [18] Zheng H, Luo Z, Fang D, Phillips FR, Lagoudas DC. Materials Letters 2012;70:109–12. [19] Chen CC, Fang D, Luo Z. Reviews in Nanoscience and Nanotechnology 2012;1:229–56. [20] Luo ZP. Metallography, Microstructure, and Analysis 2012;1:320–6. [21] Brener E, Müller-Krumbhaar H, Saito Y, Temkin D. Physical Review E 1993;47:1151–5. [22] Ma XL, Zhu YL, Zhang Z. Philosophical Magazine Letters 2002;82:461–8. [23] Yang D, Meng GW, Han FM, Zhang LD. Materials Letters 2008;62:3213–6. [24] Chen J, Wang K, Huang R, Saito T, Ikuhara YH, Hirayama T, et al. IEEE Transactions on Nanotechnology 2010;9:634–9.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Anodic-aluminum-oxide template assisted fabrication of cesium iodide (CsI) scintillator nanowires Chien Chon Chen a, Shao Fu Chang a, Zhiping Luo b,n a
Department of Energy Engineering, National United University, Miaoli 36003, Taiwan Department of Chemistry and Physics and Southeastern North Carolina Regional Microanalytical and Imaging Consortium, Fayetteville State University, Fayetteville, NC 28301, USA
b
art ic l e i nf o
a b s t r a c t
Article history: Received 1 August 2013 Accepted 4 September 2013 Available online 13 September 2013
Real-time digital imaging of radiation is realized using scintillators, and vertically aligned scintillator structures improve the spatial resolution and detection efficiency. In this work, a cost-effective approach was developed to prepare scintillator CsI nanowires in anodic aluminum oxide (AAO) nanochannels by a mechanical injection method. The AAO walls were pre-deposited with CsI nanoparticles using CsI aqueous solution to facilitate complete filling of the nanochannels. It was observed that although CsI solidifies as dendritic structures in free space on the surface of glass slides, when it is injected into the AAO nanochannels, it solidifies as stable single wires. This mechanical injection method enables fabrication of CsI nanowires with controllable size and chemical doping levels. & 2013 Elsevier B.V. All rights reserved.
Keywords: Electron microscopy Fabrication Nanowires Scintillator Solidification
1. Introduction Since the discovery of X-rays by Röntgen in 1895, radiation detection has been a rather long-time research topic that is still under development [1–3]. The traditional method to record the radiation using silver films (radiography) requires chemicals and consumables, which yields high cost and wastes to the environment. Currently the radiography is being replaced with scintillator detectors. The scintillator crystals, when excited by the radiation energy, can generate visible light that can be detected using charge-coupled device, and thereby enabling real-time digital imaging [1–3]. Thallium doped CsI scintillator is one of the brightest scintillators, with maximum wavelength of light emission around 550 nm, well suited for photodiode readout. It has been widely used for detecting X- or γ-rays. To date, the CsI(Tl) scintillators have been prepared in the following ways: (1) Traditional continuous thin foils by various deposition methods from solutions, typically containing plastic scintillator dissolved in toluene or xylene. The thin scintillator foils were obtained by solvent dissolution by flotation of the scintillator solution on water [4,5], evaporating the scintillator solution in vacuum [6], or spinning the scintillator solution on a rotating plate to obtain uniform foils [7,8].
n
Corresponding author. Tel.: þ 1 910 672 2647; fax: þ1 910 672 2420. E-mail address: [email protected] (Z. Luo).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.09.017
(2) Vertically aligned needle or micro-columnar structures [9–12] by various vapor deposition methods. Such vertically grown structures reduce the lateral spreading of light, and therefore improve the detector spatial resolution [12]. (3) Scintillators in silicon microcavities, microchannels or wells with light guides [13–15]. In a report by Rocha and Correia [13], a deep reactive-ion etching technique was used to achieve vertical side-walls with 100 mm pixel squares. However, there are several challenges associated with the current developments of these scintillator detectors, such as high cost to produce the Si microchannels which involve multiple procedures [3], and the channel size is in the order of several micrometers or larger, and there is no report on smaller channels under micrometer. In this work, a new low-cost approach to fabricate scintillator crystals using anodic aluminum oxide (AAO) rather than Si is reported, which can produce scintillator crystals with a wide range of controllable size to optimize their performance in X- or γ-ray detection. 2. Experimental procedure The starting material is high-purity aluminum (Al) substrate (99.999%). At first, the Al substrate was mechanically polished and annealed in an air furnace at 550 1C for 1 h to remove surface stress concentration. The sample was then electro-polished in a bath consisting of 15 vol% perchloric acid (HClO4, 70%), 70 vol% ethanol
C.C. Chen et al. / Materials Letters 112 (2013) 190–193
(C2H6O, 99.5%), and 15 vol% monobutylether ((CH3(CH2)3OCH2CH2OH), 85%) at applied voltage of 42 V (DC) for 10 min, using a platinum plate as a counter. The AAO with larger pores were prepared using 1 vol% H3PO4 þ5 vol% ethylene glycol (C2H4(OH)2) at 195 V and 3 1C, and smaller pores, using 3 wt% C2H2O4, at 40 V and 25 1C. After the first anodization for 40 min, the anodization film was removed in 1.8 wt% chromic acid (CrO3)þ6 vol% H3PO4 solution at 70 1C for 40 min. With regular patterns on the surfaces, the samples were used for the second anodization under the same conditions but for 1–24 h. The longer anodization time resulted deeper AAO channels. They were then widened in 5 vol% H3PO4 at 25 1C for 4 h and 1.5 h to obtain final nanopores with 450 nm and 100 nm in diameter, respectively. The microstructure and composition of the fabricated samples were studied using optical microscopy (Nikon LV 150), scanning
191
electron microscopy (SEM, JEOL 7400 and 6510 LV), X-ray energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD, PHILIPS X′Pert Pro).
3. Results and discussion Fig. 1 schematically depicts the fabrication of CsI nanowires by mechanical injection method using highly ordered AAO (Fig. 1a) as template. At first, CsI nanoparticles were deposited on AAO walls using the dip–dry method. Aqueous solution containing 1 wt% CsI was dropped on the AAO template, which was then placed on a hot plate to dry at 100 1C. It was found that CsI nanoparticles were deposited on the AAO inner walls (Fig. 1b). Since the melting point of CsI is relatively low (621 1C), the mechanical injection method [16–20] can be adopted to fabricate CsI nanowires in AAO. The schematic apparatus can be
Glass CsI Raw Material
Glass CsI Liquid
AAO
AAO/CsI
AAO/CsI
AAO/CsI
AAO/CsI
Barrier layer Al
Barrier layer Al
Barrier layer Al
Barrier layer Al
Barrier layer
Fig. 1. Schematic step-by-step fabrication procedure. (a) AAO; (b) CsI nanoparticles solidified on AAO walls, (c) before injection; (d) after injection; and (e) AAO/CsI.
Fig. 2. CsI nanoparticles (indicated) solidified on AAO walls. (a, b) SEM images; (c) XRD; and (d) EDS.
192
C.C. Chen et al. / Materials Letters 112 (2013) 190–193
found in previous publications [16,19,20]. Inside of the vacuum chamber ( 10 2 Torr) of the mechanical injection device, AAO template with CsI nanoparticles was placed on the bottom side, and raw material of CsI particles are on its top (Fig. 1c). When the device was heated up at 630 1C above the melting temperature of CsI, a hydraulic force ( 10 kgf/cm2) was applied to inject the molten CsI
into the nanopores of the AAO template (Fig. 1d). After the injection process, the chamber was kept in vacuum to cool down slowly. The remaining Al substrate can be removed mechanically, followed with dissolution in an etching solution of 10 wt% CuCl2 and 8 vol% HCl until Al is dissolved, and the solidified CsI layers covering on the top surface of AAO should also be removed mechanically (Fig. 1e).
Fig. 3. Optical images of CsI with dendritic structure solidified from 1 wt% CsI solution (a, b) and melt (c, d).
Fig. 4. SEM images of CsI nanowires. (a) Partially retained CsI on AAO; (b) CsI nanowires in AAO; (c) lateral view; and (d) cross-sectional view of CsI nanowires.
C.C. Chen et al. / Materials Letters 112 (2013) 190–193
The ionic bonds in CsI can be dissolved in a polarized H2O aqueous solution. Fig. 2 shows SEM images of CsI nanoparticles solidified on top (Fig. 2a) and bottom of AAO walls (Fig. 2b), formed by immersing AAO into 1 wt.% CsI solution and dried on a hot plat at 100 1C. The XRD pattern in Fig. 2c shows peaks from both CsI and Al substrate, as well as impurity byproducts of Al2O3 and AlPO4. The EDS spectrum (Fig. 2d) confirms the elements in CsI, as well as Al, O, C and P elements. When Al is anodized in H3PO4 containing aqueous solution, the hydrogen (H þ ) ions are absorbed on the cathode forming hydrogen gas (H2); while on the other electrode, the OH , H2 PO4 , HPO24 , and PO34 ions are absorbed on the anode and reacts with aluminum (Al3 þ ) ion forming phosphor doped aluminum hydroxide Al(OH)3) or boehmite (Al2O3 H2O) films. The film can further transform to alumina film after heat treatment. When 1 wt% CsI solution is dried on the surface of a glass slide, dendritic structures are formed, as shown in Fig. 3(a) and its enlargement in Fig. 3(b). However, when CsI is solidified from the melt (630 1C) to 25 1C on a glass slide in an air furnace, both dendrites and bubble pits are formed, as shown in Fig. 3(c) and a picture showing the pits only is presented in Fig. 3(d). Whether CsI solidifies from the aqueous solution or melt on the glass slides, dendrites can grow in the three-dimensional (3D) free space to form 3D patterns, without any external restrictions to their growth. The pits are associated with the evaporation of the melt during the solidification process. Using the AAO pre-deposited with CsI nanoparticles as template, CsI melt was mechanically injected into the AAO nanochannels to obtain larger (Fig. 4a–c) or smaller (Fig. 4d) nanowires, with diameters of 450 nm and 100 nm, respectively. In Fig. 4(a), partial CsI layer retains on top of AAO, and in Fig. 4(b), AAO is almost completely filled with CsI nanowires. From the lateral view in Fig. 4(c), the larger CsI nanowires almost filled the entire channels over the length. From the fracture of CsI-filled AAO film in Fig. 4(d), highly ordered CsI nanowires are obtained. It should be mentioned that if the CsI nanoparticles were not pre-deposited on AAO, very limited AAO nanochannels could be filled with CsI by mechanical injection. The pre-deposited CsI reduced the contact angle between the CsI melt and AAO. It is interesting that when CsI melt is confined in AAO nanochannels, it grows as stable single wires without any dendrites, consistent with the previous theoretical predictions [21]. 4. Conclusions In summary, highly ordered CsI nanowires, with diameters between 100 and 450 nm, were prepared using cost-effective mechanical injection method. Although various methods were used to fabricate different nanowires in the past [22–24], the mechanical injection method seems to be the most suitable one to fabricate the CsI nanowires which it does not require any chemical
193
precursors. Their size can be controlled by the AAO pores, and Tl doping level, by the composition of starting raw materials.
Acknowledgments This work was financially supported by the Chung-Shan Institute of Science and Technology (CSIST) under the Contract no. CSIST-442-V103. The SEM performed at SENCR-MIC was supported by FSU Faculty Startup Fund. The SENCR-MIC was funded by the U.S. Army Research Office under Contract no. W911NF-09-1-0011.
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2013.09.017. References [1] Gruner SM. Physics Today 2012;65:29–34. [2] Nikl M. Measurement Science and Technology 2006;17:R37–54. [3] Rocha JG, Lanceros-Mendez S. Recent Patents on Electrical Engineering 2011;4:1–26. [4] Yaffe L. Annual Review of Nuclear Science 1962;12:153–88. [5] Muga ML, Burnsed DJ, Steeger WE. Nuclear Instruments and Methods in Physics 1972;104:605–10. [6] Ajitanand NN, Iyengar KN. Nuclear Instruments and Methods in Physics 1976;133:71–4. [7] Norbeck E, Dubbs TP, Sobotka LG. Nuclear Instruments and Methods in Physics Research A 1987;262:546–7. [8] Weathers LW, Tsang MB. Nuclear Instruments and Methods in Physics Research A 1996;381:567–8. [9] Fujieda I, Cho G, Drewery J, Gee T, Jing T, Kaplan SN, et al. IEEE Transactions on Nuclear Science 1991;38:255–62. [10] Jing T, Goodman CA, Drewery J, Cho G, Hong WS, Lee H, et al. IEEE Transactions on Nuclear Science 1994;41:903–9. [11] Nagarkar VV, Gupta TK, Miller SR, Klugerman Y, Squillante MR, Entine G. IEEE Transactions on Nuclear Science 1998;45:492–6. [12] Nagarkar V, Gaysinskiy V. US patent 7696482 B1; 2010. [13] Rocha JG, Correia JH. Sensors and Actuators A 2001;92:203–7. [14] Badel X, Galeckas A, Linnros J, Kleimann P, Fröjdh C, Petersson CS. Nuclear Instruments and Methods in Physics Research A 2002;487:129–35. [15] Rocha JG, Ramos NF, Lanceros-Mendez S, Wolffenbuttel RF, Correia JH. Sensors and Actuators A 2004;110:119–23. [16] Chen CC, Bisrat Y, Luo ZP, Schaak RE, Chao CG, Lagoudas DC. Nanotechnology 2006;17:367–74. [17] Chen SH, Chen CC, Luo ZP, Chao CG. Materials Letters 2009;63:1165–8. [18] Zheng H, Luo Z, Fang D, Phillips FR, Lagoudas DC. Materials Letters 2012;70:109–12. [19] Chen CC, Fang D, Luo Z. Reviews in Nanoscience and Nanotechnology 2012;1:229–56. [20] Luo ZP. Metallography, Microstructure, and Analysis 2012;1:320–6. [21] Brener E, Müller-Krumbhaar H, Saito Y, Temkin D. Physical Review E 1993;47:1151–5. [22] Ma XL, Zhu YL, Zhang Z. Philosophical Magazine Letters 2002;82:461–8. [23] Yang D, Meng GW, Han FM, Zhang LD. Materials Letters 2008;62:3213–6. [24] Chen J, Wang K, Huang R, Saito T, Ikuhara YH, Hirayama T, et al. IEEE Transactions on Nanotechnology 2010;9:634–9.