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Ternary SnS(2-x)Se(x) Alloys Nanosheets and Nanosheet Assemblies with Tunable Chemical Compositions and Band Gaps for Photodetector Applications.

Yu J, Xu CY, Li Y, Zhou F, Chen XS, Hu PA, Zhen L - Sci Rep (2015)

Bottom Line: The variation tendency of band gap was also confirmed by first-principles calculations.The photoelectrochemical measurements indicate that the performance of ternary SnS(2-x)Se(x) alloys depends on their band structures and morphology characteristics.Furthermore, SnS(2-x)Se(x) photodetectors present high photoresponsivity with a maximum of 35 mA W(-1) and good light stability in a wide range of spectral response from ultraviolet to visible light, which renders them promising candidates for a variety of optoelectronic applications.

View Article: PubMed Central - PubMed

Affiliation: School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China.

ABSTRACT
Ternary metal dichalcogenides alloys exhibit compositionally tunable optical properties and electronic structure, and therefore, band gap engineering by controllable doping would provide a powerful approach to promote their physical and chemical properties. Herein we obtained ternary SnS(2-x)Se(x) alloys with tunable chemical compositions and optical properties via a simple one-step solvothermal process. Raman scattering and UV-vis-NIR absorption spectra reveal the composition-related optical features, and the band gaps can be discretely modulated from 2.23 to 1.29 eV with the increase of Se content. The variation tendency of band gap was also confirmed by first-principles calculations. The change of composition results in the difference of crystal structure as well as morphology for SnS(2-x)Se(x) solid solution, namely, nanosheets assemblies or nanosheet. The photoelectrochemical measurements indicate that the performance of ternary SnS(2-x)Se(x) alloys depends on their band structures and morphology characteristics. Furthermore, SnS(2-x)Se(x) photodetectors present high photoresponsivity with a maximum of 35 mA W(-1) and good light stability in a wide range of spectral response from ultraviolet to visible light, which renders them promising candidates for a variety of optoelectronic applications.

No MeSH data available.


Typical SEM images of SnS2−xSex alloys with different Se concentrations.(a) SnS2; (b) SnS1.66Se0.34; (c) SnS1.22Se0.78; (d) SnS0.82Se1.18; (e) SnS0.44Se1.56; (f) SnSe2.
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f2: Typical SEM images of SnS2−xSex alloys with different Se concentrations.(a) SnS2; (b) SnS1.66Se0.34; (c) SnS1.22Se0.78; (d) SnS0.82Se1.18; (e) SnS0.44Se1.56; (f) SnSe2.

Mentions: The morphology variation of SnS2−xSex alloys with Se contents was shown in Fig. 2, and the corresponding AFM and height curves were provided in Supplementary Fig. S4. Similar to our previous work32, pure SnS2 presented typical nanosheets structure with lateral sizes of ca. 0.8−1 μm and thicknesses of ca. 22 nm. The introduction of Se element would have a large affect on the morphology of the samples. Upon Se doping, nanosheets and nanosheet assemblies are formed, the later one of which consists of building block of nanosheets. When low content of Se element was introduced (x = 0.34), small NSs structure were obtained with lateral dimensions of ca. 80−160 nm and thicknesses of ca. 10−20 nm. With the increase of Se concentration, SnS1.22Se0.78 showed nanosheet shape with lateral sizes of around 400−600 nm and thicknesses of around 20−30 nm. When the value of x was 1.18, the sample would form into stacked structure (1−2 μm) composed of numerous 2D nanosheets. Interestingly, SnS0.44Se1.56 alloy owned ultrathin nanosheets structure with diameters of ca. 1.8−2.5 μm and thicknesses of ca. 8 nm with further increase of Se content (x = 1.56). The pure SnSe2 sample showed 2D layered plates structure with large sizes of several micrometers and heights of hundreds of nanometers. As shown in Fig. 2f and Supplementary Fig. S4g, SnSe2 plates were assembled by tens of individual nanosheets and the thickness of nanosheet was determined to be around 25.4 nm. The thickness variation tendency of SnS2−xSex nanosheets was approximately consistent with the crystallite sizes derived from Scherrer equation. The TEM images and SAED patterns were provided in Supplementary Fig. S5. The nanosheets structure of SnS1.22Se0.78, SnS0.44Se1.56, and SnSe2 were in good agreement with the SEM and AFM results. Remarkably, the pure SnS232 and SnSe2 are single crystalline and own 2D layered structure with hexagonal symmetry. However, the diffraction rings of polycrystalline would appear with the introduction of Se element. The tunable composition may provide a good candidate for photodector applications. As we know, the crystal growth habits and environmental factors would play a critical role in crystallization process33. Layered SnS2 and SnSe2 are both isostructural with typical CdI2−type structure. According to our previous work32, the synthesis approach in this work would provide a favorable environmental to induce tin dichalcogenides to grow along lateral direction and expose (001) facets. Consequently, we believe the ternary SnS2−xSex alloys would prefer to grow and form 2D nanosheets structure. However, the practical growth environment may affect the self-assembling behavior. The (001) orientation is preferentially oriented for pure SnS232, and that of SnSe2 is (101) facet19. The different crystal orientation might result in synergistic effect on the crystal growth of ternary alloys. The competition phenomenon was especially obvious in SnS0.82Se1.18 nanosheets assemblies, which owned nearly equal S and Se concentrations in the initial stage of chemical reaction (in view of the incomplete dissolution of add Se). Before the solvothermal reaction, all of the reactants were dissolved in the TEG. However, it is difficult to understand the exact reaction mechanism during such a fast reaction. The detailed mechanism of nanosheets and nanosheets assemblies is still under investigation.


Ternary SnS(2-x)Se(x) Alloys Nanosheets and Nanosheet Assemblies with Tunable Chemical Compositions and Band Gaps for Photodetector Applications.

Yu J, Xu CY, Li Y, Zhou F, Chen XS, Hu PA, Zhen L - Sci Rep (2015)

Typical SEM images of SnS2−xSex alloys with different Se concentrations.(a) SnS2; (b) SnS1.66Se0.34; (c) SnS1.22Se0.78; (d) SnS0.82Se1.18; (e) SnS0.44Se1.56; (f) SnSe2.
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Related In: Results  -  Collection

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f2: Typical SEM images of SnS2−xSex alloys with different Se concentrations.(a) SnS2; (b) SnS1.66Se0.34; (c) SnS1.22Se0.78; (d) SnS0.82Se1.18; (e) SnS0.44Se1.56; (f) SnSe2.
Mentions: The morphology variation of SnS2−xSex alloys with Se contents was shown in Fig. 2, and the corresponding AFM and height curves were provided in Supplementary Fig. S4. Similar to our previous work32, pure SnS2 presented typical nanosheets structure with lateral sizes of ca. 0.8−1 μm and thicknesses of ca. 22 nm. The introduction of Se element would have a large affect on the morphology of the samples. Upon Se doping, nanosheets and nanosheet assemblies are formed, the later one of which consists of building block of nanosheets. When low content of Se element was introduced (x = 0.34), small NSs structure were obtained with lateral dimensions of ca. 80−160 nm and thicknesses of ca. 10−20 nm. With the increase of Se concentration, SnS1.22Se0.78 showed nanosheet shape with lateral sizes of around 400−600 nm and thicknesses of around 20−30 nm. When the value of x was 1.18, the sample would form into stacked structure (1−2 μm) composed of numerous 2D nanosheets. Interestingly, SnS0.44Se1.56 alloy owned ultrathin nanosheets structure with diameters of ca. 1.8−2.5 μm and thicknesses of ca. 8 nm with further increase of Se content (x = 1.56). The pure SnSe2 sample showed 2D layered plates structure with large sizes of several micrometers and heights of hundreds of nanometers. As shown in Fig. 2f and Supplementary Fig. S4g, SnSe2 plates were assembled by tens of individual nanosheets and the thickness of nanosheet was determined to be around 25.4 nm. The thickness variation tendency of SnS2−xSex nanosheets was approximately consistent with the crystallite sizes derived from Scherrer equation. The TEM images and SAED patterns were provided in Supplementary Fig. S5. The nanosheets structure of SnS1.22Se0.78, SnS0.44Se1.56, and SnSe2 were in good agreement with the SEM and AFM results. Remarkably, the pure SnS232 and SnSe2 are single crystalline and own 2D layered structure with hexagonal symmetry. However, the diffraction rings of polycrystalline would appear with the introduction of Se element. The tunable composition may provide a good candidate for photodector applications. As we know, the crystal growth habits and environmental factors would play a critical role in crystallization process33. Layered SnS2 and SnSe2 are both isostructural with typical CdI2−type structure. According to our previous work32, the synthesis approach in this work would provide a favorable environmental to induce tin dichalcogenides to grow along lateral direction and expose (001) facets. Consequently, we believe the ternary SnS2−xSex alloys would prefer to grow and form 2D nanosheets structure. However, the practical growth environment may affect the self-assembling behavior. The (001) orientation is preferentially oriented for pure SnS232, and that of SnSe2 is (101) facet19. The different crystal orientation might result in synergistic effect on the crystal growth of ternary alloys. The competition phenomenon was especially obvious in SnS0.82Se1.18 nanosheets assemblies, which owned nearly equal S and Se concentrations in the initial stage of chemical reaction (in view of the incomplete dissolution of add Se). Before the solvothermal reaction, all of the reactants were dissolved in the TEG. However, it is difficult to understand the exact reaction mechanism during such a fast reaction. The detailed mechanism of nanosheets and nanosheets assemblies is still under investigation.

Bottom Line: The variation tendency of band gap was also confirmed by first-principles calculations.The photoelectrochemical measurements indicate that the performance of ternary SnS(2-x)Se(x) alloys depends on their band structures and morphology characteristics.Furthermore, SnS(2-x)Se(x) photodetectors present high photoresponsivity with a maximum of 35 mA W(-1) and good light stability in a wide range of spectral response from ultraviolet to visible light, which renders them promising candidates for a variety of optoelectronic applications.

View Article: PubMed Central - PubMed

Affiliation: School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China.

ABSTRACT
Ternary metal dichalcogenides alloys exhibit compositionally tunable optical properties and electronic structure, and therefore, band gap engineering by controllable doping would provide a powerful approach to promote their physical and chemical properties. Herein we obtained ternary SnS(2-x)Se(x) alloys with tunable chemical compositions and optical properties via a simple one-step solvothermal process. Raman scattering and UV-vis-NIR absorption spectra reveal the composition-related optical features, and the band gaps can be discretely modulated from 2.23 to 1.29 eV with the increase of Se content. The variation tendency of band gap was also confirmed by first-principles calculations. The change of composition results in the difference of crystal structure as well as morphology for SnS(2-x)Se(x) solid solution, namely, nanosheets assemblies or nanosheet. The photoelectrochemical measurements indicate that the performance of ternary SnS(2-x)Se(x) alloys depends on their band structures and morphology characteristics. Furthermore, SnS(2-x)Se(x) photodetectors present high photoresponsivity with a maximum of 35 mA W(-1) and good light stability in a wide range of spectral response from ultraviolet to visible light, which renders them promising candidates for a variety of optoelectronic applications.

No MeSH data available.