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High-Quality Luminescent Tellurium Nanowires of Several Nanometers in Diameter and High Aspect Ratio Synthesized by a Poly (Vinyl Pyrrolidone)-Assisted Hydrothermal Process Hai-Sheng Qian, Shu-Hong Yu,* Jun-Yan Gong, Lin-Bao Luo, and Lin-feng Fei DiVision of Nanomaterials & Chemistry, Hefei National Laboratory for Physical Sciences at Microscale, Structural Research Laboratory of CAS, School of Chemistry and Materials, UniVersity of Science and Technology of China, Hefei 230026, People’s Republic of China ReceiVed NoVember 10, 2005. In Final Form: February 9, 2006 Large-scale selective synthesis of uniform single crystalline tellurium nanowires with a diameter of 4-9 nm, and microbelts with a width of 250-800 nm and tens of micrometers in length, can be realized by a poly (vinyl pyrrolidone) (PVP)-assisted hydrothermal process. The formation of tellurium nanowires and nanobelts in the presence of PVP is strongly dependent on the reaction conditions such as temperature, the amount of PVP, and reaction time. The results demonstrated that the keys for selective synthesis of Te nanobelts and nanowires are to modulate the growth rates of (100), (101), and (110) planes in the presence of PVP and to precisely control the reaction kinetics. High-quality luminescent ultrathin t-Te nanowires with a diameter of 4-9 nm display strong luminescent emission in the blue-violet region. This approach provides a facile route for the production of high-quality tellurium nanostructures with an interesting optical property. Furthermore, the synthesized ultrathin nanowires with deep blue color and nanobelts in gray color by this approach can be well dispersed in water or ethanol, making it possible for further engineering of their surfaces to prepare other hybrid core-shell nanostructures.
1. Introduction In past decades, fabrication of nanomaterials with a controllable size and shape is of great scientific and technological interest.1 Elemental tellurium is a narrow direct band gap semiconducting material with a band gap energy of 0.35 eV, which has a highly anisotropic growth tendency because of its unique helical-chain conformation in its crystal structure. Crystalline tellurium shows interesting optical properties and may be used as a holographic recording material, an infrared photoconductive detector, and for nonlinear-infrared optics, such as second harmonic generation.2 Many techniques have been designed to synthesize tellurium nanostructures, especially for one-dimensional nanostructures including nanowires, nanorods, nanotubes, and nanobelts, for instance, electrochemical and electrophoretic deposition,3 microwave-assisted synthesis,4 physical evaporation,5 decomposition of TeCl4 conducted in polydecene in the presence of trioctylphosphine oxide (TOPO) as a surfactant at 250-300 °C,6 self-seeding solution process,7,8 polyol process,9 and surfactantassisted hydrothermal method in an ethanol/water media.10 * Corresponding author. Fax: + 86 551 3603040. E-mail: shyu@ ustc.edu.cn. (1) (a) Ahmadi, T. S.; Wang, Z. L.; Green, T. C.; Henglein, A.; EI-Sayed, M. A. Science 1996, 272, 1924. (b) Peng, X. G.; Manna, L.; Yang, W. D.; Wickham, J.; Scher, E.; Kadavanich, A.; Alivisatos, A. P. Nature 2000, 404, 59. (b) Lieber, C. M. Solid State Commun. 1998, 107, 607. (c) Hu, J. T.; Odom, T. W.; Lieber, C. M. Acc. Chem. Res. 1999, 32, 435. (d) Yang, P. D.; Wu, Y. Y.; Fan, R. Int. J. Nano. 2002, 1, 1. (e) Xia, Y.; Yang, P.; Sun, Y.; Wu, Y.; Mayer, B.; Gates, B.; Yin, Y.; Kim, F.; Yan, H. AdV. Mater. 2003, 5, 353. (2) (a) Shih, I.; Champness, C. H. J. Cryst. Growth 1978, 44, 492. (b) Beauvais, R.; Lessard, A.; Galarneau, P.; Knystautas, E. J. Appl. Phys. Lett. 1990, 57, 1354. (3) Zhao, A. W.; Ye, C. H.; Meng, G. W.; Zhang, L. D.; Ajayan, P. M. J. Mater. Res. 2003, 18, 2318. (4) Zhu, Y. J.; Wang, W. W.; Qi, R. J.; Hu, X. L. Angew. Chem., Int. Ed. 2004, 43, 1410. (5) Li, X. L.; Cao, G. H.; Feng, C. M.; Li, Y. D. J. Mater. Chem. 2004, 14, 244. (6) Yu, H.; Gibbons, P. C.; Buhro, W. E. J. Mater. Chem. 2004, 14, 595. (7) Gautam, U. K.; Rao, C. N. R. J. Mater. Chem. 2004, 14, 2530. (8) Mayers, B.; Xia, Y. N. J. Mater. Chem. 2002, 12, 1875. (9) Mayers, B.; Xia, Y. N. AdV. Mater. 2002, 14, 279.
Recently, a chemical vapor deposition method has been developed to synthesize tellurium nanobelts with a width ranging from 50 to 300 nm in bulk quantity from Al2Te3 powder and H2O.11 A controlled hydrothermal route has been developed to synthesize single crystalline tellurium nanobelts with an average thickness of ca. 8 nm and a width of 30-500 nm, and nanotubes by in situ disproportionation of sodium tellurite in aqueous ammonia at about 180 °C.12 More recently, biomolecules such as aliginic acid and amino acids have been used as additives for the controlled synthesis of Te nanowires,13 and scrolled tellurium nanotubes.14 Te nanowires with a diameter of 100 nm can be spontaneously formed in solution through chemical decomposition of stabilizer-depleted CdTe nanoparticles in the presence of a strong complex agent.15 However, to our best knowledge, tellurium nanowires with a diameter below 10 nm have not been achieved so far. Poly (vinyl pyrrolidone) (PVP, polymerization degree 360) has been successfully employed as a stabilizing agent as well as a structure directing agent for the preparation of silver nanoparticles (including nanowires).16 Liu and co-workers found that PVP had a steric effect on the growth of tellurium along the [0001] direction and the long polyvinyl chain of PVP may be responsible for this effect.10a In this paper, we report a facile route for the selective synthesis of tellurium nanowires and microbelts by a PVP-assisted (10) (a) Liu, Z. P.; Li, S.; Yang, Y.; Hu, Z. K.; Peng, S.; Liang, J. B.; Qian, Y. T. New J. Chem. 2003, 27, 1748. (b) Liu, Z. P.; Hu, Z. K.; Liang, J. B.; Li, S.; Yang, Y.; Peng, S.; Qian, Y. T. Langmuir 2004, 20, 214. (11) Geng, B. Y.; Lin, Y.; Peng, X. S.; Meng, G. W.; Zhang, L. D. Nanotechnology 2003, 14, 983. (12) Mo, M. S.; Zeng, J. H.; Liu, X. M.; Yu, W. C.; Zhang, S. Y.; Qian, Y. T. AdV. Mater. 2002, 14, 1658. (13) Lu, Q. Y.; Gao, F.; Komarneni, S. AdV. Mater. 2004, 16, 1629. (14) He, Z. B.; Yu, S. H.; Zhu, J. P. Chem. Mater. 2005, 17, 2785. (15) Tang, Z. Y.; Wang, Y.; Sun, K.; Kotov, N. A. AdV. Mater. 2005, 17, 358. (16) (a) Zhang, Z. T.; Zhao, B.; Hu, L. M. J. Solid State Chem. 1996, 121, 105. (b) Sun, Y. G.; Yin, Y. D.; Mayers, B.; Herricks, T.; Xia, Y. N. Chem. Mater. 2002, 14, 4736. (c) Yin, Y. D.; Li, Z. Y.; Zhong, Z. Y.; Gates, B.; Xia, Y. N.; Venkateswaran, S. J. Mater. Chem. 2002, 12, 522.
10.1021/la053021l CCC: $33.50 © 2006 American Chemical Society Published on Web 03/15/2006
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Figure 1. XRD pattern of as-prepared product from reduction of Na2TeO3 (0.5 mmol) in the presence of N2H4OH used as a reducing agent with the addition of 0.6 g of PVP. The reaction was done at 180 °C for 24 h.
hydrothermal process under mild conditions. Especially, uniform ultrathin tellurium nanowires with a diameter of only a few nanometers can be synthesized in large quantity, which show a highly luminescent property in the blue-violet region. To our best knowledge, the nanowires with narrow diameters have not been achieved so far. The influence of reaction temperature, reaction time, and the amount of polymer surfactant on the formation of tellurium nanostructures has been systematically examined in such a reaction system. 2. Experimental Section All chemicals are of analytical grade, which are commercially available from Shanghai Chemical Reagent Co. Ltd and used in this study without further purification. Synthesis of Nanobelts. In a typical synthesis, 0.6 g of PVP was put into a Teflon-lined stainless steel autoclave with a volume capacity of 30 mL and dissolved in 15 mL of double distilled water under vigorous magnetic stirring to form a homogeneous solution at room temperature. After that, 0.1107 g of sodium tellurite (Na2TeO3, 0.5 mmol) was put into that solution and dissolved, and then 1 mL of hydrazine hydrate (85%, w/w %) and 2 mL of aqueous ammonia solution (25-28%, w/w %) were added into the mixed solution, respectively. The final solution was clear, and 6 mL of double distilled water was added again to up to 80% capacity of the total volume of the Teflon vessel (the total volume of the reaction solution is 24 mL). The container was closed and maintained at 180 °C for 24 h. After that, the autoclave was cooled to room temperature naturally. The final product in silver-gray was centrifuged and washed several times with double distilled water and absolute ethanol, and dried in a vacuum at 60 °C for 6 h. Synthesis of Ultrathin Te Nanowires. The procedures for the synthesis of 4-9 nm nanowires are similar to those for microbelts, which have been described in a previous section. When the reaction had proceeded for 4 h, it was cooled to room temperature rapidly with cold tap water. After that, 40 mL of acetone was added into the final solution and the product was precipitated. The product was centrifuged and washed with absolute alcohol and double distilled water several times. Characterization. The obtained sample was characterized on an (Philips X’Pert Pro Super) X-ray powder diffractometer with Cu Ka radiation (λ ) 1.541874 Å). The morphology was examined with a JEOL JSM-6700F scanning electron microscope (SEM), a transmission electron microscope (TEM) performed on a Hitachi (Tokyo, Japan) H-800 transmission electron microscope (TEM) at an accelerating voltage of 200 kV, and a high-resolution transmission electron microscope (HRTEM) (JEOL-2010) operated at an acceleration voltage of 200 kV. Photoluminescence (PL) emission was performed at room temperature with a Perkin-Elmer LS55 luminescence spectrometer. UV-vis spectra were recorded on UV2501PC/2550 at room temperature (Shimadzu Corp., Japan).
Figure 2. (a-c) TEM images of tellurium microbelts obtained from 0.5 mmol of sodium tellurite in 2 mL of aqueous ammonia solution, 1 mL of hydrate hydrazine, and with the addition of 0.6 g of PVP at 180 °C for 24 h. The inset shows the corresponding ED obtained from the marked area of the same microbelt; the electron beam was focused along [11h0] axis. (d) A high-resolution TEM image obtained from the edge of an individual microbelt (shown in Figure 2c). The fringe spacing of 5.9 Å corresponds to the interplanar distance of {001} planes, implying that the growth direction of this microbelt was [001].
Figure 3. The influence of the amount of PVP on the tellurium nanostructures. TEM images of four samples prepared in 2 mL of aqueous ammonia solution, 1 mL of hydrate hydrazine, 180 °C, 24 h, in the presence of PVP, showing the morphology evolution of the tellurium with the addition of different amounts of PVP: (a) 0 g, (b) 0.2 g, (c) 0.4 g, (d) 1.2 g.
3. Results and Discussion 3.1. Selective Synthesis of Tellurium Nanobelts and Nanowires: Influence of the Amount of PVP. Figure 1 shows the X-rays diffraction (XRD) pattern of the products obtained from reduction of sodium tellurite (0.5 mmol) in the presence
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Figure 4. (a) TEM of an individual nanowire that was taken from the sample shown in Figure 3b. (b) A lattice resolved HRTEM image showing lattice spacings of 5.9, 4.0, and 3.2 Å were observed, respectively, and were taken from the edge of the nanowire shown in (a). The fringes with a spacing of 0.59 nm that were observed, which are perpendicular to the axial direction, imply that the nanowire grew along [001]. (c) SAED pattern taken on the nanowire. The electron beam was focused along [010] axis.
of 1 mL (85%, w/w %) of hydrazine hydrate via the PVP-assisted hydrothermal process; all peaks can be indexed to the hexagonal phase of tellurium (t-Te) with a cell constant and a ) 4.456 Å, c ) 5.922 Å, and without impurity peaks detected, which are in good agreement with the standard literature data (JCPDF card number: 36-1452). Unusually strong (h00) reflection peaks and weak (hkl) reflection peaks (l10) were still observed in the XRD pattern, while (hk0) reflection peaks (k10) were all relatively weak, indicating that the particles might have preferential orientation along specific directions, which need to be further confirmed by high-resolution electron microscopy (HRTEM) and selective area electron diffraction (SAED analysis. Tellurium microbelts with a width ranging from hundreds of nanometers to several micrometers, and tens of micrometers to hundreds of micrometers in length, and a few nanometers in thickness can be produced, and a few nanowires were observed (Figure 2a). Figure 2b clearly indicated that the microbelts were very thin, and the high-resolution transmission electron microscopy (HRTEM) image and electron diffraction (ED) pattern of a single microbelt were shown in Figure 2d,e, revealing that the as-prepared microbelts were single crystalline with a growth direction along [001] and are free from defects and dislocations. The formation of nanobelts is in good agreement with that reported previously.11,12 In the present case, no nanowires can be obtained and instead aggregated particles are obtained in the absence of PVP (Figure 3a), which could be due to too fast reaction speed in the presence of a strong reducing agent at 180 °C. A previous report has shown that only spherical particles were obtained by reducing TeO2 using NaBH4 as a reducing agent with the addition of a low amount of PVP via microwave heating.4 However, uniform nanowires can be produced in the presence of a suitable amount of PVP here. When the amount of PVP increased to 0.2 g, uniform nanowires with a diameter of ca. 20 nm were obtained (Figure 3b). When the amount of PVP increased up to 0.4 g, the product is composed of not only nanowires with several nanometers in diameter, but also nanobelts with width ranging from tens of diameters to several hundred nanometers (Figure 3c). However, further increasing the amount of the PVP will result in increasing the size of the particles, and microbelts with several micrometers in diameters are obtained when the amount of PVP increased to 0.6 g (Figure 2). In addition, the product became poor in quality, and a mixture composed of nanowires, nanobelts, and large rodlike and sheetlike particles with diverse sizes is produced if the amount of PVP increased up to 1.2 g (Figure 3d). These results suggested that the suitable amount of PVP played a key role in producing tellurium nanostructures with different sizes and shapes, as well as the homogeneity of particles. The shapes and sizes of the Te
Figure 5. The influence of reaction time on the shapes and sizes of tellurium nanostructures. TEM images of the samples prepared in 2 mL of aqueous ammonia solution, and 1 mL of hydrate hydrazine with the addition of 0.6 g of PVP at 180 °C, showing the morphology evolution of the tellurium nanostructures. The reaction time was, respectively, (a) 4 h, (b) 6 h, and (c) 12 h.
Figure 6. XRD pattern of the ultrathin nanowires obtained from the reaction of sodium tellurite (Na2TeO3, 0.5 mmol) with hydrazine hydrate at 180 °C for 4 h.
nanostructures are strongly dependent on the reaction kinetics and the amount of the PVP. A HRTEM image in Figure 4b was taken from the edge of the single nanowire shown in Figure 4a, showing lattice spacings of ca. 5.9, 4.0, and 3.2 Å, respectively, corresponding to the lattice spacings of the (001), (100), and (101) planes for trigonal tellurium, respectively. Also, the angle of the planes of (001) and (101) is 55.4°, which is consistent with that calculated result according to its crystal structure. Figure 4c shows the corresponding ED pattern of the nanowires, which was obtained by focusing the electron beam along the [010] axis. Both HRTEM and SAED patterns confirmed that the axis of the nanowire is
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Figure 7. (a) TEM image of the ultrathin Te nanowires, (b) the histogram of the diameter distribution of the ultrathin nanowires, (c) a selected area diffraction pattern of the ultrathin Te nanowires, and (d) a lattice resolved HRTEM image taken on an individual ultrathin nanowire with a diameter of 7 nm.
along [001] direction, and the nanowire was structurally uniform and no dislocation was detected in the examined area. 3.2. Controlled Synthesis of Ultrathin Tellurium Nanowires: Influence of Reaction Time. The above results suggested that the quality of the product is strongly dependent on the reaction time even though the amount of PVP is within a suitable range. Ultrathin and uniform nanowires with 4-9 nm in diameters and length up to hundreds of micrometers can be produced when the reaction was carried out for 4 h, and after that the autoclave was cooled to room temperature rapidly (Figure 5a). To our best knowledge, such ultrathin Te nanowires have not been synthesized so far. When the reaction was carried out for 6-12 h, the number of nanobelts increased (Figure 5b,c). With time further prolonged, more nanobelts with wide width will form as shown in Figure 2. The above time-dependent shape evolution process of the nanobelts suggested that ultrathin nanowires formed at the initial stage tend to grow further preferentially along certain crystallographic directions. The XRD pattern in Figure 6 shows that all of the diffraction peaks become widened. The intensities of the (100) and (110) peaks are much intensified as compared to that in the literature. The ultrathin nanowires and their crystallinity have been examined by HRTEM observations. Figure 7a,b showed the uniform nanowires with an average diameter of 7 nm, which is in well agreement with the results calculated according to the Scherer equation (dm ) kλ/β1/2 cos θ). The diameter distribution of the nanowires was shown in Figure 7b. The ultrathin nanowires are single crystalline as demonstrated by the selected area diffraction pattern shown in Figure 7c. The HRTEM images in Figure 7d clearly showed the lattice spacings of 5.8 and 3.2 Å, corresponding to those for (001) and (101) planes, respectively. Again, the enhanced diffraction intensities of (100) and (110) faces (Figure 6) underlie that the ultrathin
nanowires formed at the initial stage already start growing in a highly preferential way as we discussed above. In addition, the resulting size differences under hydrothermal conditions are due to the Ostwald ripening process.17 In this process, the formation of tiny crystalline nuclei in a supersaturated medium occurs first and then is followed by crystal growth, in which the larger particles will grow at the cost of the small ones due to the surface energy difference between them. 3.3. Influence of Temperature on Growth of Tellurium Nanostructures. Temperature is another important factor, which cannot be ignored. Lower temperature does not favor the growth of uniform nanowires even though the amount of PVP is within the suitable region. The product obtained at 120 °C for 24 h is a mixture of nanowires and nanobelts with diverse sizes as shown in Figure 8a. In contrast, the sample synthesized at 220 °C for 24 h is composed of relatively uniform but shorter nanorods with a length of tens of micrometers. Interestingly, the majority of nanorods are of unequal diameter as shown in a typical TEM image in Figure 8b,c. The selected area diffraction patterns in Figure 8d,e taken in different areas of the singe nanorod (marked with white circles in Figure 8c) indicated that both the thinner part and the thicker part of the nanorod are perfect single crystalline with the same growth direction along [001]. It is supposed that the nanorods formed shorter in length and with the homogeneity in diameter due to rapidly nucleation and growth at higher temperature. In short, different tellurium nanostructures can be selectively synthesized and realized by adjusting different temperatures and amounts of PVP. 3.4. Possible Growth Mechanism of Tellurium Nanostructures. PVP, as a polymer surfactant, has been proved to play an important role in the synthesis of one-dimensional nanorods and nanowires of tellurium.4,10a In fact, the effects of (17) Sugimoto, T. AdV. Colloid Interface Sci. 1987, 28, 65.
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Figure 8. TEM images of two samples prepared in 2 mL of aqueous ammonia solution, 1 mL of hydrate hydrazine, and with the addition of 0.6 g of PVP at different temperatures for 24 h: (a) 120 °C, (b) and (c) 220 °C. Parts (d) and (e) show the ED patterns taken on the specific areas marked in (c) of a typical nanowire with different diameters.
PVP on the synthesis of tellurium nanostructures are rather complicated. HRTEM observation and the electron diffraction pattern suggested that both (101) lattice spacings and the diffraction spot for (101) face are missing on the sample of the nanobelts, while (101) lattice spacings and the diffraction spot for (101) appear in the sample of nanowires (Figure 2 and Figure 4b,c). The enhanced growth rate along the [110] direction is responsible for the formation of nanobelts. It is, however, possible that the nanostructures are growing along both the axis of the nanowire, the [100] direction, and the [110] direction, but that the growth rate along the [100] direction exceeds that along the [110] direction. The microbelts were observed after an extended period of growth, thus enhancing the observed growth along the [110] to a noticeable extent. Furthermore, the selective adsorption of PVP on the specific planes such as (100), (101), and (110) will result in differences in their growth rates. Thus, we can conclude that the keys for selective synthesis of Te nanobelts and nanowires are to modulate the growth rates of {100}, {101}, and {110} planes in the presence of PVP and to precisely control the reaction kinetics. 3.5. Optical Properties of Ultrathin Tellurium Nanowires and Nanobelts. The dispersion of ultrathin Te nanowires in water gives a deep blue color, which is dramatically different from the gray color usually observed for Te nanostructures reported previously (see insets in Figure 9). The unusual color of ultrathin Te nanowires suggested that the optical property is dramatically different from those of bulk materials and other nanostructures with relative large sizes.
Figure 9. Typical TEM images of (a) ultrathin Te nanowires and (b) nanobelts. The inset shows the color of the ultrathin nanowires and nanobelts, which were dispersed in water.
The UV-vis absorption spectrum of the nanobelts with gray color does not have an absorption peak in the range of 250-800 nm. However, the UV-vis spectrum for the ultrathin nanowires with deep blue color shows two broad typical absorption peaks located at 278 and 586 nm, respectively (Figure 10). The absorption peak at 278 nm (4.46 eV) is due to the allowed direct transition from the valence band (p-bonding triplet) to the conduction band (p-antibonding triplet), and another broad but strong absorption peak centered at 586 nm (2.12 eV) can be assigned to a forbidden direction transition.18,19 However, the origin of this absorption peak is still not clear at present.7 In addition, the UV-vis absorption bands are also quite similar to those reported for the thin films by Swan et al.19 Photoluminescence of tellurium nanostructures has been rarely studied previously. Room-temperature photoluminescence spectroscopy studies indicated that the nanobelts with a width of 250-800 nm do not give emission with excitation wavelengths of 365 nm as reported by Rao et al.7 The excitation spectrum of the ultrathin nanowires shows two strong peaks at 267 and 365 nm, respectively, under the wavelength of 455 nm (Figure 11a). (18) Isomaski, H. M. J. von Boehm. Phys. Scr. 1982, 25, 801. (19) Swan, R.; Ray, A. K.; Hogarth, C. A. Phys. Status Solidi A 1991, 127, 555.
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Figure 10. UV-vis spectra of (a) the nanobelts with a width of 250-800 nm, and (b) the nanowires with 4-9 nm in diameter, respectively.
Two strong photoluminescence emission peaks in the blue-violet region (390-550 nm) with the excitation wavelength of 365 nm were observed for the ultrathin nanowires with dark blue color, which have not been reported previously (Figure 11b). The deconvolution of the strong and broad peak gives three Gaussian components with three peaks at 410, 433, and 452 nm. The emission peak around 700 nm was not observed even though it was recorded with an excitation wavelength of 300 nm as described by Rao and co-workers.7 To our best knowledge, it is the first observation that ultrathin Te nanowires synthesized by the present approach can give blue-violet emissions. The strong optical properties in the blue-violet region observed here suggested that the ultrathin Te nanowires could have applications in the future. The detailed optical property of this kind of nanostructures needs to be further investigated.
4. Conclusions In summary, selective synthesis of uniform single crystalline tellurium nanowires with a diameter of 4-9 nm, and microbelts with a width of 250-800 nm and tens of micrometers in length, can be easily realized by a poly (vinyl pyrrolidone) (PVP)-assisted hydrothermal process. The formation of tellurium nanostructures with various forms is strongly dependent on the temperature, the amount of PVP, and reaction time. The keys for selective synthesis of Te nanobelts and nanowires are to modulate the growth rates of (100), (101), and (110) planes in the presence of PVP and to precisely control the reaction kinetics in the present synthetic system. Interestingly, high-quality ultrathin t-Te nanowires with a diameter of 4-9 nm display strong luminescent emission in the blue-violet region. This approach provides an efficient route for the production of high-quality tellurium nanostructures with an interesting optical property. Furthermore, the synthesized ultrathin nanowires with deep blue color and nanobelts in gray color by this approach can be well dispersed in water or ethanol, making it possible for further engineering of their surfaces20 to prepare other hybrid core-shell nanostructures such as hybrid
Figure 11. The optical property of tellurium nanowires with 4-9 nm in diameter. (a) The excitation spectrum of the ultrathin Te nanowires obtained under an emission wavelength of 435 nm. (b) Photoluminescence spectrum (black line) recorded with an excitation wavelength of 365 nm. The deconvolution of the band gave three Gaussian components with peaks at 411, 433, and 452 nm, as shown by the dashed blue lines. All of the spectra were obtained at room temperature.
nanocables or to be used as templates for templating other nanostructures. Further investigation is still underway and will be reported in due course.
Acknowledgment. This work is supported by special funding from the Centurial Program of Chinese Academy of Sciences, the National Science Foundation of China (NSFC) (grant nos. 20325104, 20321101, 50372065), the Scientific Research Foundation for the Returned Overseas Chinese Scholars, the Specialized Research Fund for the Doctoral Program (SRFDP) of Higher Education State Education Ministry, and the PartnerGroup of the Chinese Academy of Sciences-the Max Planck Society. LA053021L
(20) Caruso, F. AdV. Mater. 2001, 13, 11.
