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Facile microwave-assisted synthesis of Klockmannite CuSe nanosheets and their exceptional electrical properties.

Liu YQ, Wang FX, Xiao Y, Peng HD, Zhong HJ, Liu ZH, Pan GB - Sci Rep (2014)

Bottom Line: This is ascribed to the quantum size effect of NS and the presence of Schottky barrier.In addition, the influence of the molar ratio of Cu(2+)/SeO2, reaction temperature, and reaction time on the growth of CuSe NSs is explored.The template effect of oleylamine and the intrinsic crystal nature of CuSe NS are proposed to account for the growth of hexagonal CuSe NSs.

View Article: PubMed Central - PubMed

Affiliation: Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, 215123 Suzhou, P. R. China.

ABSTRACT
Klockmannite copper selenide nanosheets (CuSe NSs) are synthesized by a facile microwave-assisted method and fully characterized. The nanosheets have smooth surface and hexagonal shape. The lateral size is 200-500 nm × 400-800 nm and the thickness is 55 ± 20 nm. The current-voltage characteristics of CuSe NS films show unique Ohmic and high-conducting behaviors, comparable to the thermally-deposited gold electrode. The high electrical conductivity of CuSe NSs implies their promising applications in printed electronics and nanodevices. Moreover, the local electrical variation is observed, for the first time, within an individual CuSe NS at low bias voltages (0.1 ~ 3 V) by conductive atomic force microscopy (C-AFM). This is ascribed to the quantum size effect of NS and the presence of Schottky barrier. In addition, the influence of the molar ratio of Cu(2+)/SeO2, reaction temperature, and reaction time on the growth of CuSe NSs is explored. The template effect of oleylamine and the intrinsic crystal nature of CuSe NS are proposed to account for the growth of hexagonal CuSe NSs.

No MeSH data available.


(a–d) FE-SEM images and (e) XRD patterns of the products prepared with the different molar ratios of Cu2+ to SeO2: (a) 0.5:1, (b) 1:1, (c) 2:1 and (d) 4:1. The diffraction peaks are marked by: (•) klockmannite hexagonal CuSe, JCPDS No. 34-0171; (○) berzelianite cubic Cu2Se, JCPDS No. 88-2044 and (◊) cubic Cu, JCPDS No. 03-1018.
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f4: (a–d) FE-SEM images and (e) XRD patterns of the products prepared with the different molar ratios of Cu2+ to SeO2: (a) 0.5:1, (b) 1:1, (c) 2:1 and (d) 4:1. The diffraction peaks are marked by: (•) klockmannite hexagonal CuSe, JCPDS No. 34-0171; (○) berzelianite cubic Cu2Se, JCPDS No. 88-2044 and (◊) cubic Cu, JCPDS No. 03-1018.

Mentions: Fig. 4 shows a set of typical SEM images and XRD patterns of the products obtained at different molar ratios of Cu2+ to SeO2, while the other parameters are fixed. Quasi-circular and truncated-triangular nanoplates are formed at a molar ratio of 0.5:1 (Fig. 4a), while hexagonal NSs are obtained at a molar ratio of 1:1 (Fig. 4b). The XRD patterns (Fig. 4e) confirm that both nanoplates and nanosheets have the same klockmannite phase. Note that instead of discrete ones, the nanoplates are prone to stack with each other. Similar phenomenon is observed for berzelianite nanoplates in the literature22. When the molar ratio is increased to 2:1 (Fig. 4c), berzelianite Cu2Se nanowires with the diameter of 30 ± 10 nm and the length of several micrometers become dominant (Fig. S4a). The typical lattice spacing is ~3.32 Å (Fig. S4b), which is consistent with the (111) plane spacing of cubic berzelianite Cu2Se phase (JCPDS No. 88-2044, a = 5.787 Å, Fm-3m). Further increasing the molar ratio to 4:1, a mixture of nanoparticles and nanorods is obtained (Fig. 4d). The XRD pattern reveals a blend of berzelianite Cu2Se and Cu. The berzelianite Cu2Se phase is confirmed by HR-TEM (Fig. S4d) and a lattice spacing of 3.3 Å is revealed. Nevertheless, the formation of Cu phase is due to the reduction of excessive Cu2+ by oleylamine (OM) and the lack of SeO2 source. The above results indicate that the molar ratio of Cu2+ to SeO2 play an important role in the morphology and crystal phase of the final products. This is likely due to different redox reaction rates under different kinetic conditions. Highly anisotropic structures tend to become favorable in a slow reduction process3132. Specifically, with a molar ratio of 2:1, Cu2+ ions are reduced by OM into Cu+ ions, which can react with SeO2. The resultant cubic Cu2Se tends to grow into nanowires due to the anisotropic growth. When the molar ratio is 4:1, the reaction rate increases remarkably and more Cu2Se seeds emerge, favoring the isotropic growth in the early stage. As the reaction proceeds, a number of Cu2+ ions are consumed, thereby resulting in lower reduction rates. Meanwhile, the isotropic growth is switched to the anisotropic one, leading to the formation of Cu2Se nanorods.


Facile microwave-assisted synthesis of Klockmannite CuSe nanosheets and their exceptional electrical properties.

Liu YQ, Wang FX, Xiao Y, Peng HD, Zhong HJ, Liu ZH, Pan GB - Sci Rep (2014)

(a–d) FE-SEM images and (e) XRD patterns of the products prepared with the different molar ratios of Cu2+ to SeO2: (a) 0.5:1, (b) 1:1, (c) 2:1 and (d) 4:1. The diffraction peaks are marked by: (•) klockmannite hexagonal CuSe, JCPDS No. 34-0171; (○) berzelianite cubic Cu2Se, JCPDS No. 88-2044 and (◊) cubic Cu, JCPDS No. 03-1018.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4126004&req=5

f4: (a–d) FE-SEM images and (e) XRD patterns of the products prepared with the different molar ratios of Cu2+ to SeO2: (a) 0.5:1, (b) 1:1, (c) 2:1 and (d) 4:1. The diffraction peaks are marked by: (•) klockmannite hexagonal CuSe, JCPDS No. 34-0171; (○) berzelianite cubic Cu2Se, JCPDS No. 88-2044 and (◊) cubic Cu, JCPDS No. 03-1018.
Mentions: Fig. 4 shows a set of typical SEM images and XRD patterns of the products obtained at different molar ratios of Cu2+ to SeO2, while the other parameters are fixed. Quasi-circular and truncated-triangular nanoplates are formed at a molar ratio of 0.5:1 (Fig. 4a), while hexagonal NSs are obtained at a molar ratio of 1:1 (Fig. 4b). The XRD patterns (Fig. 4e) confirm that both nanoplates and nanosheets have the same klockmannite phase. Note that instead of discrete ones, the nanoplates are prone to stack with each other. Similar phenomenon is observed for berzelianite nanoplates in the literature22. When the molar ratio is increased to 2:1 (Fig. 4c), berzelianite Cu2Se nanowires with the diameter of 30 ± 10 nm and the length of several micrometers become dominant (Fig. S4a). The typical lattice spacing is ~3.32 Å (Fig. S4b), which is consistent with the (111) plane spacing of cubic berzelianite Cu2Se phase (JCPDS No. 88-2044, a = 5.787 Å, Fm-3m). Further increasing the molar ratio to 4:1, a mixture of nanoparticles and nanorods is obtained (Fig. 4d). The XRD pattern reveals a blend of berzelianite Cu2Se and Cu. The berzelianite Cu2Se phase is confirmed by HR-TEM (Fig. S4d) and a lattice spacing of 3.3 Å is revealed. Nevertheless, the formation of Cu phase is due to the reduction of excessive Cu2+ by oleylamine (OM) and the lack of SeO2 source. The above results indicate that the molar ratio of Cu2+ to SeO2 play an important role in the morphology and crystal phase of the final products. This is likely due to different redox reaction rates under different kinetic conditions. Highly anisotropic structures tend to become favorable in a slow reduction process3132. Specifically, with a molar ratio of 2:1, Cu2+ ions are reduced by OM into Cu+ ions, which can react with SeO2. The resultant cubic Cu2Se tends to grow into nanowires due to the anisotropic growth. When the molar ratio is 4:1, the reaction rate increases remarkably and more Cu2Se seeds emerge, favoring the isotropic growth in the early stage. As the reaction proceeds, a number of Cu2+ ions are consumed, thereby resulting in lower reduction rates. Meanwhile, the isotropic growth is switched to the anisotropic one, leading to the formation of Cu2Se nanorods.

Bottom Line: This is ascribed to the quantum size effect of NS and the presence of Schottky barrier.In addition, the influence of the molar ratio of Cu(2+)/SeO2, reaction temperature, and reaction time on the growth of CuSe NSs is explored.The template effect of oleylamine and the intrinsic crystal nature of CuSe NS are proposed to account for the growth of hexagonal CuSe NSs.

View Article: PubMed Central - PubMed

Affiliation: Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, 215123 Suzhou, P. R. China.

ABSTRACT
Klockmannite copper selenide nanosheets (CuSe NSs) are synthesized by a facile microwave-assisted method and fully characterized. The nanosheets have smooth surface and hexagonal shape. The lateral size is 200-500 nm × 400-800 nm and the thickness is 55 ± 20 nm. The current-voltage characteristics of CuSe NS films show unique Ohmic and high-conducting behaviors, comparable to the thermally-deposited gold electrode. The high electrical conductivity of CuSe NSs implies their promising applications in printed electronics and nanodevices. Moreover, the local electrical variation is observed, for the first time, within an individual CuSe NS at low bias voltages (0.1 ~ 3 V) by conductive atomic force microscopy (C-AFM). This is ascribed to the quantum size effect of NS and the presence of Schottky barrier. In addition, the influence of the molar ratio of Cu(2+)/SeO2, reaction temperature, and reaction time on the growth of CuSe NSs is explored. The template effect of oleylamine and the intrinsic crystal nature of CuSe NS are proposed to account for the growth of hexagonal CuSe NSs.

No MeSH data available.