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Surface-roughness-assisted formation of large-scale vertically aligned CdS nanorod arrays via solvothermal method
Applied Surface Science 273 (2013) 89–93
Contents lists available at SciVerse ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Surface-roughness-assisted formation of large-scale vertically aligned CdS nanorod arrays via solvothermal method Minmin Zhou a , Shancheng Yan a,b,∗ , Yi Shi a,∗∗ , Meng Yang a , Huabin Sun a , Jianyu Wang a , Yao Yin a , Fan Gao a a b
National Laboratory of Solid State Microstructures, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, PR China School of Geography and Biological Information, Nanjing University of Posts and Telecommunications, Nanjing 210046, PR China
a r t i c l e
i n f o
Article history: Received 19 September 2012 Received in revised form 15 January 2013 Accepted 25 January 2013 Available online 4 February 2013 Keywords: CdS nanorod Surface roughness Seed layer Solvothermal reaction
a b s t r a c t Large-scale cadmium sulfide (CdS) nanorod arrays were successfully synthesized on several different substrates through solvothermal reaction. During the growth experiments, we observed that the adhesion strength of the CdS nanorod arrays to different substrates differed dramatically, causing some of the CdS coating being easily flushed away by deionized water (DI water). With doubts and suspicions, we seriously investigate the original morphology of all the substrates by using atomic force microscopy (AFM). The phase, morphology, crystal structure and photoelectric property of all the products were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and current–voltage (I–V) probe station. The growth mechanism of solvothermal reaction was proposed on the basis of all the characterizations. Our approach presents a universal method of liquid phase epitaxy of 1D material on a wide range of substrates of any shape. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Low-dimensional nanostructured materials such as graphene, nanowires, carbon nanotubes and quantum dots have drawn significant interests in the science community for decades for their unique optical and mechanical properties. Among low-dimensional materials, one-dimensional (1D) materials have particular potential for device application ranging from broad-band light-emitting diodes (LEDs) and lasers [1] to biochemical sensors [2] due to their readily tunable optical, electrical and nanomechanical properties [3]. CdS, a direct bandgap material with Eg of 2.42 eV at room temperature, can be widely used for photoelectronic devices such as solar cells [4], LEDs [5], optical antennas [6], etc. Various methods for the preparation of 1D CdS have been developed as chemical vapor deposition [7], solvothermal reaction [8,9,20,22], electrochemical synthesis [10] and thermal evaporation [11]. The properties of the 1D CdS [4,7,11] as well as CdS incorporated composites [9,12–14] or heterostructures with other materials [10,15–18] have been well studied so far. But how the surface
∗ Corresponding author at: National Laboratory of Solid State Microstructures, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, PR China. Tel.: +86 25 83621220. ∗∗ Corresponding author. E-mail addresses: [email protected] (S. Yan), [email protected] (Y. Shi). 0169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2013.01.191
properties of the substrate affect the synthesis of 1D CdS has been little explored previously. In this work, we investigate the growth mechanism of largescale vertically aligned CdS nanorod arrays on different substrates via a facile solvothermal routine [8]. It turned out that the morphology of the selected substrate was quite critical for the adhesion intensity between the CdS seed layers and the substrate. We believe the adhesion difference originates from the key property of the substrate, that is, surface roughness. By this approach, we proposed a possible formation mechanism of the solvothermal synthesis of a wide range of 1D nanomaterials. Moreover, this work points out a very promising way to fabricate heterostructures readily.
2. Experimental 2.1. Synthesis of CdS nanorods All the chemicals used were of analytical grade and purchased from Nanjing Wanqing Chemical Glassware Instrument Co. LTD. In a typical procedure, 1 mmol of cadmium nitrate Cd(NO3 )2 ·4H2 O, 3 mmol of thiourea and 0.6 mmol of glutathione were dissolved in a Teflon-lined stainless autoclave filled with 40 ml DI water. After placing a prepared substrate inside, the clave was sealed and maintained at 200 ◦ C for 3.5 h and then cooled down to room
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Fig. 1. SEM, TEM images, and I–V curves of CdS nanorods grown on self-prepared ITO-glass substrate (sample 1). (a) SEM image of CdS nanorods array with the magnification of 20 K. (b) TEM image of an individual CdS nanorod. (c) HRTEM image of the area marked a red rectangular in (b). (d) I–V curves with and without illumination. (For interpretation of the references to color in figure legend, the reader is referred to the web version of the article.)
temperature. At last, the produced samples were rinsed with DI water and dried naturally. 2.2. Characterization All the samples’ phase compositions were examined by Xray diffractometer D/max 2500VL/PC with Cu K␣ radiation. SEM images were acquired on a SEM LEO 1550. Transmission electron microscopy (JEOL 2100) was applied to confirm the crystallinity and the growth orientation of the CdS nanorods. Raman spectrometer (JY T64000) was operated by a 50 mW and 514.5 wavelength Ar green laser to study the phonon vibration. AFM height images were taken on a Veeco Multimode8, showing the original morphology of all the substrates. I–V test was performed on an Aglient 4156C parameter analyzer. 3. Results and discussion In this paper, we adopted five different substrates for the experiments: self-prepared indium tin oxide (ITO)-glass through electron beam evaporation (EBE), silicon wafer, purchased ITO-glass, AuITO-glass (purchased ITO-glass coated with thin Au film) and naked glass. After the synthesis process of CdS nanorod arrays, the final products were labeled as sample 1, 2, 3, 4 and 5, accordingly. Fig. 1 shows the SEM, TEM images and I–V test result of sample 1. It is clearly seen from Fig. 1a that the substrate is fully coated with high-ordered CdS nanorods, most of which are vertical to the substrate. High-resolution TEM (HRTEM) image (Fig. 1c) was taken of the red rectangular area in Fig. 1b. The lattice plane spaces were calculated to be 0.67 nm, corresponding to the lattice constants of c-axis of wurtzite CdS [19], which indicates clearly that the growth is along the [0 0 1] orientation. Basic I–V characterization was carried out on a probe station for testing the electrical and photoconductive properties of the CdS nanorod arrays. Each
sample had a non-linear I–V characteristic for a −2 V to 2 V sweep. Fig. 1d is a representative graph of sample 1. Obviously, under white light illumination the output current of the nanorods increased at least by one order of magnitude compared to measurements in dark conditions, showing a strong potential in photovoltaic applications. Fig. 2a–d are the SEM images of the CdS nanorod arrays synthesized on the other four substrates. We found that the parameters of the nanorods were nearly of the same size (about 100 nm) no matter what the substrate was. Moreover, all the CdS nanorods were vertically well-aligned except for sample 2 (Fig. 2a), which definitely have some connection with the surface condition of silicon wafer. Fig. 2e–f are the TEM images of the CdS nanorods scratched off from sample 4 (Fig. 2c). The HRTEM image (Fig. 2f) taken of the red rectangular area in Fig. 2e clearly reveals a set of fringes for (0 0 2) planes of wurtzite CdS with a lattice spacing of about 0.33 nm [20], in accordance with the conclusion above that the [0 0 1] direction is the preferential growth orientation. X-ray diffraction (XRD) patterns of CdS nanorod arrays grown on all the substrates were collected in Fig. 3 with the diffraction angle 2 ranging from 10◦ to 90◦ . All the diffraction peaks can be assigned to wurtzite CdS [21] with the exception of the high peak in sample 1 attributed to ITO film [22], some of the strong and sharp peaks in sample 2 attributed to silicon wafer and the peak in sample 4 attributed to Au film [23]. Beyond contemplation, the corresponded ITO diffraction peak of sample 3, 4 were much weaker than sample 1. We attribute that to the larger thickness (∼500 nm) and higher quality of the self-prepared ITO-glass by EBE. Furthermore, the CdS nanorod arrays exhibit much stronger reflection at [0 0 2] direction as revealed from the XRD patterns, which in another way suggest that the CdS nanorods grew preferentially oriented along the c-axis. Although all the five substrates support the growth of CdS nanorod arrays, the stabilities of the final products differ
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Fig. 2. SEM & TEM images of CdS nanorods grown on other substrates, all the SEM images were taken with the same magnification as Fig. 1a. (a) SEM image of CdS nanorods array on Si wafer (sample 2) (b) SEM image of CdS nanorods array on purchased ITO-glass (sample 3) (c) SEM image of CdS nanorods array on Au-ITO-glass (sample 4) (d) SEM image of CdS nanorods array on naked glass (sample 5). (e) TEM image of CdS nanorods synthesized on Au-ITO-glass substrate. (f) HRTEM image of the area marked with a red rectangular in e.
Fig. 3. XRD patterns of CdS nanorods synthesized on the five substrates.
significantly. Roughly speaking, the CdS nanorod arrays formed on the silicon wafer (sample 2) or naked glass (sample 5) were very unstable and could be easily flushed away by DI water. We trust that it was related with some specific property of the substrates. To find out the relation between the sample stability and the substrate, the original morphology information of all the five substrates was recorded by atomic force microscopy (AFM), as shown in the Fig. 4. And the root-mean-square (rms) roughness values were also given in the following Table 1. As seen in Table 1, the rms value of the substrate of sample 5 is much lower than the others, which may be the cause of the weak adhesion. Unexpectedly, silicon wafer with the highest rms value did not support a strong adhesion with the seed layer. We assumed that the surface of silicon wafer is smooth but not flat, which could cause the great rms value but weak adhesion with the CdS seed layer. The corresponding AFM profiles of all the substrates were shown in Fig. 5 from which we can clearly find out that sample 2 and sample 5 were much smoother than the other three samples. It directly proves the above hypothesis we proposed about the surface condition of silicon wafer. In general, during the initial period of the solvothermal reaction, CdS seed crystals were synthesized and deposited on the substrate,
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Fig. 4. 1 m × 1 m AFM height images of all the substrates.
Fig. 5. AFM profiles of all the substrates with the data collected along the green lines in Fig. 4a–e. (For interpretation of the references to color in figure legend, the reader is referred to the web version of the article.)
more likely in the concaves. In an aqueous solution sufficient of cadmium and sulfer, the CdS seed crystals grew into little CdS nanorods and formed a quasi-two dimension CdS thin film known as the seed layer. It would not be difficult to understand the adhesion strength of the CdS seed layer to the substrate was critically determined by the surface roughness. However, the growth process of those rods that did not have proper orientation was restricted from each other in long axis and largely slowed down by the capping agent-glutathione in short axis [8,24]. So the final result turned out that only these rods that had proper orientation succeeded to complete the growth as shown in Fig. 6. Under this mechanism, it is easier to draw the conclusion that only these substrates with greater surface roughness can support firm formation of nanorod arrays (Fig. 7).To study the information about the vibration modes to measure the CdS crystallinity and confirm the crystal structure, room-temperature Raman characterization was performed. The Raman spectra of all the products were put in Fig. 5 with the wave number varies from 200 cm−1 to 800 cm−1 . Two characteristic bands of wurtzite CdS nanorods [25], positioned at 294 cm−1 and 593 cm−1 , can be clearly seen from the Raman spectra of all the
Fig. 6. Schematic illustrations for the growth process of CdS nanorods array via solvothermal method.
M. Zhou et al. / Applied Surface Science 273 (2013) 89–93
[3] [4]
[5] [6]
[7]
[8]
[9]
Fig. 7. Raman spectra of CdS nanorods synthesized on the five substrates.
five samples. Taken altogether, the intensity of the 1LO (Longitudinal optical) was much stronger than the 2LO. Furthermore, the intensity ratios of I1LO/2LO of the all the products did not vary much (∼7), indicating that the high crystallinity of the CdS nanorods was irrelevant with the substrate adopted.
[10]
[11]
[12]
4. Conclusions
[13]
In summary, CdS nanorod arrays can be synthesized on various substrates through solvothermal reaction in the present work. The results indicated that the surface roughness of the substrate plays a key role in determining the adhesion force between the CdS seed layer and the substrate. Moreover, the parameters of the CdS nanorods synthesized on substrates with different surface roughness were almost the same size. We believe that this approach can be expanded to any substrate of any shape, which provides a very promising way to fabricate heterostructures conveniently.
[14]
Acknowledgements This work was financially supported by the National Basic Research Program of China (973 Program: 2013CB932903), the National Science Foundations of China (No. 61205057), China Postdoctoral Science Special Foundation (2012T50488), China Postdoctoral Science Foundation (2011M500896), Natural Science Foundation of Education Bureau of Jiangsu Province (12KJB180009), Jiangsu Planned Projects for Postdoctoral Research Funds (1102015C), the Open Research Fund of State Key Laboratory of Bioelectronics, Southeast University, the open research fund of Key Laboratory of MEMS of Ministry of Education, Southeast University, and the Scientific Research Foundation of Nanjing University of Posts and Telecommunications (NY210083).
[15]
[16]
[17]
[18] [19]
[20]
[21]
[22]
[23]
[24]
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Contents lists available at SciVerse ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Surface-roughness-assisted formation of large-scale vertically aligned CdS nanorod arrays via solvothermal method Minmin Zhou a , Shancheng Yan a,b,∗ , Yi Shi a,∗∗ , Meng Yang a , Huabin Sun a , Jianyu Wang a , Yao Yin a , Fan Gao a a b
National Laboratory of Solid State Microstructures, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, PR China School of Geography and Biological Information, Nanjing University of Posts and Telecommunications, Nanjing 210046, PR China
a r t i c l e
i n f o
Article history: Received 19 September 2012 Received in revised form 15 January 2013 Accepted 25 January 2013 Available online 4 February 2013 Keywords: CdS nanorod Surface roughness Seed layer Solvothermal reaction
a b s t r a c t Large-scale cadmium sulfide (CdS) nanorod arrays were successfully synthesized on several different substrates through solvothermal reaction. During the growth experiments, we observed that the adhesion strength of the CdS nanorod arrays to different substrates differed dramatically, causing some of the CdS coating being easily flushed away by deionized water (DI water). With doubts and suspicions, we seriously investigate the original morphology of all the substrates by using atomic force microscopy (AFM). The phase, morphology, crystal structure and photoelectric property of all the products were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and current–voltage (I–V) probe station. The growth mechanism of solvothermal reaction was proposed on the basis of all the characterizations. Our approach presents a universal method of liquid phase epitaxy of 1D material on a wide range of substrates of any shape. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Low-dimensional nanostructured materials such as graphene, nanowires, carbon nanotubes and quantum dots have drawn significant interests in the science community for decades for their unique optical and mechanical properties. Among low-dimensional materials, one-dimensional (1D) materials have particular potential for device application ranging from broad-band light-emitting diodes (LEDs) and lasers [1] to biochemical sensors [2] due to their readily tunable optical, electrical and nanomechanical properties [3]. CdS, a direct bandgap material with Eg of 2.42 eV at room temperature, can be widely used for photoelectronic devices such as solar cells [4], LEDs [5], optical antennas [6], etc. Various methods for the preparation of 1D CdS have been developed as chemical vapor deposition [7], solvothermal reaction [8,9,20,22], electrochemical synthesis [10] and thermal evaporation [11]. The properties of the 1D CdS [4,7,11] as well as CdS incorporated composites [9,12–14] or heterostructures with other materials [10,15–18] have been well studied so far. But how the surface
∗ Corresponding author at: National Laboratory of Solid State Microstructures, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, PR China. Tel.: +86 25 83621220. ∗∗ Corresponding author. E-mail addresses: [email protected] (S. Yan), [email protected] (Y. Shi). 0169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2013.01.191
properties of the substrate affect the synthesis of 1D CdS has been little explored previously. In this work, we investigate the growth mechanism of largescale vertically aligned CdS nanorod arrays on different substrates via a facile solvothermal routine [8]. It turned out that the morphology of the selected substrate was quite critical for the adhesion intensity between the CdS seed layers and the substrate. We believe the adhesion difference originates from the key property of the substrate, that is, surface roughness. By this approach, we proposed a possible formation mechanism of the solvothermal synthesis of a wide range of 1D nanomaterials. Moreover, this work points out a very promising way to fabricate heterostructures readily.
2. Experimental 2.1. Synthesis of CdS nanorods All the chemicals used were of analytical grade and purchased from Nanjing Wanqing Chemical Glassware Instrument Co. LTD. In a typical procedure, 1 mmol of cadmium nitrate Cd(NO3 )2 ·4H2 O, 3 mmol of thiourea and 0.6 mmol of glutathione were dissolved in a Teflon-lined stainless autoclave filled with 40 ml DI water. After placing a prepared substrate inside, the clave was sealed and maintained at 200 ◦ C for 3.5 h and then cooled down to room
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Fig. 1. SEM, TEM images, and I–V curves of CdS nanorods grown on self-prepared ITO-glass substrate (sample 1). (a) SEM image of CdS nanorods array with the magnification of 20 K. (b) TEM image of an individual CdS nanorod. (c) HRTEM image of the area marked a red rectangular in (b). (d) I–V curves with and without illumination. (For interpretation of the references to color in figure legend, the reader is referred to the web version of the article.)
temperature. At last, the produced samples were rinsed with DI water and dried naturally. 2.2. Characterization All the samples’ phase compositions were examined by Xray diffractometer D/max 2500VL/PC with Cu K␣ radiation. SEM images were acquired on a SEM LEO 1550. Transmission electron microscopy (JEOL 2100) was applied to confirm the crystallinity and the growth orientation of the CdS nanorods. Raman spectrometer (JY T64000) was operated by a 50 mW and 514.5 wavelength Ar green laser to study the phonon vibration. AFM height images were taken on a Veeco Multimode8, showing the original morphology of all the substrates. I–V test was performed on an Aglient 4156C parameter analyzer. 3. Results and discussion In this paper, we adopted five different substrates for the experiments: self-prepared indium tin oxide (ITO)-glass through electron beam evaporation (EBE), silicon wafer, purchased ITO-glass, AuITO-glass (purchased ITO-glass coated with thin Au film) and naked glass. After the synthesis process of CdS nanorod arrays, the final products were labeled as sample 1, 2, 3, 4 and 5, accordingly. Fig. 1 shows the SEM, TEM images and I–V test result of sample 1. It is clearly seen from Fig. 1a that the substrate is fully coated with high-ordered CdS nanorods, most of which are vertical to the substrate. High-resolution TEM (HRTEM) image (Fig. 1c) was taken of the red rectangular area in Fig. 1b. The lattice plane spaces were calculated to be 0.67 nm, corresponding to the lattice constants of c-axis of wurtzite CdS [19], which indicates clearly that the growth is along the [0 0 1] orientation. Basic I–V characterization was carried out on a probe station for testing the electrical and photoconductive properties of the CdS nanorod arrays. Each
sample had a non-linear I–V characteristic for a −2 V to 2 V sweep. Fig. 1d is a representative graph of sample 1. Obviously, under white light illumination the output current of the nanorods increased at least by one order of magnitude compared to measurements in dark conditions, showing a strong potential in photovoltaic applications. Fig. 2a–d are the SEM images of the CdS nanorod arrays synthesized on the other four substrates. We found that the parameters of the nanorods were nearly of the same size (about 100 nm) no matter what the substrate was. Moreover, all the CdS nanorods were vertically well-aligned except for sample 2 (Fig. 2a), which definitely have some connection with the surface condition of silicon wafer. Fig. 2e–f are the TEM images of the CdS nanorods scratched off from sample 4 (Fig. 2c). The HRTEM image (Fig. 2f) taken of the red rectangular area in Fig. 2e clearly reveals a set of fringes for (0 0 2) planes of wurtzite CdS with a lattice spacing of about 0.33 nm [20], in accordance with the conclusion above that the [0 0 1] direction is the preferential growth orientation. X-ray diffraction (XRD) patterns of CdS nanorod arrays grown on all the substrates were collected in Fig. 3 with the diffraction angle 2 ranging from 10◦ to 90◦ . All the diffraction peaks can be assigned to wurtzite CdS [21] with the exception of the high peak in sample 1 attributed to ITO film [22], some of the strong and sharp peaks in sample 2 attributed to silicon wafer and the peak in sample 4 attributed to Au film [23]. Beyond contemplation, the corresponded ITO diffraction peak of sample 3, 4 were much weaker than sample 1. We attribute that to the larger thickness (∼500 nm) and higher quality of the self-prepared ITO-glass by EBE. Furthermore, the CdS nanorod arrays exhibit much stronger reflection at [0 0 2] direction as revealed from the XRD patterns, which in another way suggest that the CdS nanorods grew preferentially oriented along the c-axis. Although all the five substrates support the growth of CdS nanorod arrays, the stabilities of the final products differ
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Fig. 2. SEM & TEM images of CdS nanorods grown on other substrates, all the SEM images were taken with the same magnification as Fig. 1a. (a) SEM image of CdS nanorods array on Si wafer (sample 2) (b) SEM image of CdS nanorods array on purchased ITO-glass (sample 3) (c) SEM image of CdS nanorods array on Au-ITO-glass (sample 4) (d) SEM image of CdS nanorods array on naked glass (sample 5). (e) TEM image of CdS nanorods synthesized on Au-ITO-glass substrate. (f) HRTEM image of the area marked with a red rectangular in e.
Fig. 3. XRD patterns of CdS nanorods synthesized on the five substrates.
significantly. Roughly speaking, the CdS nanorod arrays formed on the silicon wafer (sample 2) or naked glass (sample 5) were very unstable and could be easily flushed away by DI water. We trust that it was related with some specific property of the substrates. To find out the relation between the sample stability and the substrate, the original morphology information of all the five substrates was recorded by atomic force microscopy (AFM), as shown in the Fig. 4. And the root-mean-square (rms) roughness values were also given in the following Table 1. As seen in Table 1, the rms value of the substrate of sample 5 is much lower than the others, which may be the cause of the weak adhesion. Unexpectedly, silicon wafer with the highest rms value did not support a strong adhesion with the seed layer. We assumed that the surface of silicon wafer is smooth but not flat, which could cause the great rms value but weak adhesion with the CdS seed layer. The corresponding AFM profiles of all the substrates were shown in Fig. 5 from which we can clearly find out that sample 2 and sample 5 were much smoother than the other three samples. It directly proves the above hypothesis we proposed about the surface condition of silicon wafer. In general, during the initial period of the solvothermal reaction, CdS seed crystals were synthesized and deposited on the substrate,
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Fig. 4. 1 m × 1 m AFM height images of all the substrates.
Fig. 5. AFM profiles of all the substrates with the data collected along the green lines in Fig. 4a–e. (For interpretation of the references to color in figure legend, the reader is referred to the web version of the article.)
more likely in the concaves. In an aqueous solution sufficient of cadmium and sulfer, the CdS seed crystals grew into little CdS nanorods and formed a quasi-two dimension CdS thin film known as the seed layer. It would not be difficult to understand the adhesion strength of the CdS seed layer to the substrate was critically determined by the surface roughness. However, the growth process of those rods that did not have proper orientation was restricted from each other in long axis and largely slowed down by the capping agent-glutathione in short axis [8,24]. So the final result turned out that only these rods that had proper orientation succeeded to complete the growth as shown in Fig. 6. Under this mechanism, it is easier to draw the conclusion that only these substrates with greater surface roughness can support firm formation of nanorod arrays (Fig. 7).To study the information about the vibration modes to measure the CdS crystallinity and confirm the crystal structure, room-temperature Raman characterization was performed. The Raman spectra of all the products were put in Fig. 5 with the wave number varies from 200 cm−1 to 800 cm−1 . Two characteristic bands of wurtzite CdS nanorods [25], positioned at 294 cm−1 and 593 cm−1 , can be clearly seen from the Raman spectra of all the
Fig. 6. Schematic illustrations for the growth process of CdS nanorods array via solvothermal method.
M. Zhou et al. / Applied Surface Science 273 (2013) 89–93
[3] [4]
[5] [6]
[7]
[8]
[9]
Fig. 7. Raman spectra of CdS nanorods synthesized on the five substrates.
five samples. Taken altogether, the intensity of the 1LO (Longitudinal optical) was much stronger than the 2LO. Furthermore, the intensity ratios of I1LO/2LO of the all the products did not vary much (∼7), indicating that the high crystallinity of the CdS nanorods was irrelevant with the substrate adopted.
[10]
[11]
[12]
4. Conclusions
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In summary, CdS nanorod arrays can be synthesized on various substrates through solvothermal reaction in the present work. The results indicated that the surface roughness of the substrate plays a key role in determining the adhesion force between the CdS seed layer and the substrate. Moreover, the parameters of the CdS nanorods synthesized on substrates with different surface roughness were almost the same size. We believe that this approach can be expanded to any substrate of any shape, which provides a very promising way to fabricate heterostructures conveniently.
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Acknowledgements This work was financially supported by the National Basic Research Program of China (973 Program: 2013CB932903), the National Science Foundations of China (No. 61205057), China Postdoctoral Science Special Foundation (2012T50488), China Postdoctoral Science Foundation (2011M500896), Natural Science Foundation of Education Bureau of Jiangsu Province (12KJB180009), Jiangsu Planned Projects for Postdoctoral Research Funds (1102015C), the Open Research Fund of State Key Laboratory of Bioelectronics, Southeast University, the open research fund of Key Laboratory of MEMS of Ministry of Education, Southeast University, and the Scientific Research Foundation of Nanjing University of Posts and Telecommunications (NY210083).
[15]
[16]
[17]
[18] [19]
[20]
[21]
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[24]
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