Size dependence of structural metastability in semiconductor nanocrystals

Science

Volumn 276, Issue 5311, 1997, Pages 398-401

  Chen, Chia Chun ^a,b   Herhold, A B ^a   Johnson, C S ^a   Alivisatos, A P ^a  

^a UNIVERSITY OF CALIFORNIA   (United States)

^b NATIONAL CHUNG CHENG UNIVERSITY   (Taiwan)

Author keywords

[No Author keywords available]

Indexed keywords

CADMIUM; NANOPARTICLE; SELENIDE; SULFIDE;

ANISOTROPY; ARTICLE; CHEMICAL REACTION KINETICS; CRYSTAL; CRYSTAL STRUCTURE; PHASE TRANSITION; PRESSURE; PRIORITY JOURNAL; SEMICONDUCTOR; SOLID STATE; TEMPERATURE; X RAY POWDER DIFFRACTION;

EID: 0030963445     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.276.5311.398     Document Type: Article

References (38)

1. Q. Xia, H. Xia, A. L. Ruoff, J. Appl. Phys. 73, 8198 (1993).
2. T. Li et al., Phys. Rev. Lett. 74, 5232 (1995).
3. L. E. Brus, J. A. W. Harkless, F. H. Stillinger, J. Am. Chem. Soc. 118, 4834 (1996).
4. D. Turnbull, J. Chem. Phys. 20, 411 (1952); Solid State Phys. 3, 225 (1956).
5. D. Turnbull, J. Chem. Phys. 20, 411 (1952); Solid State Phys. 3, 225 (1956).
6. J. M. Besson et al., Phys. Rev. B 44, 4214 (1991).
7. U. D. Venkateswaran, L. J. Cui, B. A. Weinstein, ibid. 45, 9237 (1992).
8. K. Mizushima, S. Yip, E. Kaxiras, ibid. 50, 14952 (1994).
9. J. C. Jamieson, Science 139, 762 (1963); B. A. Weinstein and G. J. Piermarini, Phys. Rev. B 12, 1172 (1975).
10. J. C. Jamieson, Science 139, 762 (1963); B. A. Weinstein and G. J. Piermarini, Phys. Rev. B 12, 1172 (1975).
11. A well-defined thermodynamic constraint was placed on the system in these studies: An extended crystal may be viewed as having been divided into separate nanometer-size crystals, each of the same size, and with no possibility of atoms migrating between them. Under these conditions, the nanocrystals have a well-defined, size-dependent phase diagram, with an extra term compared to the case for the bulk solid to take account of the surface. This constraint (no communication between crystallites) was carefully observed under all the conditions reported here.
12. A. N. Goldstein, C. M. Echer, A. P. Alivisatos, Science 256, 1425 (1992).
13. S. H. Tolbert and A. P. Alivisatos, ibid. 265, 373 (1994); Annu. Rev. Phys. Chem. 46, 595 (1995).
14. S. H. Tolbert and A. P. Alivisatos, ibid. 265, 373 (1994); Annu. Rev. Phys. Chem. 46, 595 (1995).
15. _, J. Chem. Phys. 102, 4642 (1995).
16. S. H. Tolbert, A. B. Herhold, L. E. Brus, A. P. Alivisatos, Phys. Rev. Lett. 76, 4384 (1996).
17. We achieved high pressures and temperatures using a Merrill-Bassett diamond anvil cell heated in a ceramic oven. The main body of the cell including bolts and screws was made from Inconel 718 to reduce thermal expansion effects, which caused a decrease in pressure of less than 0.5 GPa when experiments were carried out up to 13 GPa and 500 K. We measured pressures using standard ruby fluorescence techniques [J. D. Bamett, S. Block, G. J. Piermarini, Rev. Sci. Instrum. 44, 1 (1973)]. Temperatures were measured with a thermocouple in contact with the steel gasket. High-pressure and high-temperature x-ray diffraction was performed on wiggler beam line 10-2 at the Stanford Synchrotron Radiation Laboratory with a photon energy of 20 KeV. We collected diffraction patterns in the angle-dispersive mode using image plates; these patterns were angle-integrated to obtain the data shown here [J. H. Nguyen and R. Jeanloz, ibid. 64, 3456 (1993)]. In all cases the instrument resolution was far greater than the intrinsic diffraction linewidths because of the small crystallite size. We collected optical absorption spectra using a scanning ultraviolet-visible spectrometer with 2-nm resolution in 6 to 7 min. Optical transitions in wurtzite nanocrystals are electronically allowed, and the absorption consists of a series of discrete features in the visible region. Rock-salt nanocrystals have a band gap in the near-infrared, and the transitions are electronically forbidden but phonon-assisted, as in the bulk material [S. H. Tolbert, A. B. Herhold, C. S. Johnson, A. P. Alivisatos, Phys. Rev. Lett. 73, 3266 (1994)], resulting in a featureless absorption spectrum. We observed an abrupt change in the electronic absorption, a clear signature of the phase transition.
18. We achieved high pressures and temperatures using a Merrill-Bassett diamond anvil cell heated in a ceramic oven. The main body of the cell including bolts and screws was made from Inconel 718 to reduce thermal expansion effects, which caused a decrease in pressure of less than 0.5 GPa when experiments were carried out up to 13 GPa and 500 K. We measured pressures using standard ruby fluorescence techniques [J. D. Bamett, S. Block, G. J. Piermarini, Rev. Sci. Instrum. 44, 1 (1973)]. Temperatures were measured with a thermocouple in contact with the steel gasket. High-pressure and high-temperature x-ray diffraction was performed on wiggler beam line 10-2 at the Stanford Synchrotron Radiation Laboratory with a photon energy of 20 KeV. We collected diffraction patterns in the angle-dispersive mode using image plates; these patterns were angle-integrated to obtain the data shown here [J. H. Nguyen and R. Jeanloz, ibid. 64, 3456 (1993)]. In all cases the instrument resolution was far greater than the intrinsic diffraction linewidths because of the small crystallite size. We collected optical absorption spectra using a scanning ultraviolet-visible spectrometer with 2-nm resolution in 6 to 7 min. Optical transitions in wurtzite nanocrystals are electronically allowed, and the absorption consists of a series of discrete features in the visible region. Rock-salt nanocrystals have a band gap in the near-infrared, and the transitions are electronically forbidden but phonon-assisted, as in the bulk material [S. H. Tolbert, A. B. Herhold, C. S. Johnson, A. P. Alivisatos, Phys. Rev. Lett. 73, 3266 (1994)], resulting in a featureless absorption spectrum. We observed an abrupt change in the electronic absorption, a clear signature of the phase transition.
19. We achieved high pressures and temperatures using a Merrill-Bassett diamond anvil cell heated in a ceramic oven. The main body of the cell including bolts and screws was made from Inconel 718 to reduce thermal expansion effects, which caused a decrease in pressure of less than 0.5 GPa when experiments were carried out up to 13 GPa and 500 K. We measured pressures using standard ruby fluorescence techniques [J. D. Bamett, S. Block, G. J. Piermarini, Rev. Sci. Instrum. 44, 1 (1973)]. Temperatures were measured with a thermocouple in contact with the steel gasket. High-pressure and high-temperature x-ray diffraction was performed on wiggler beam line 10-2 at the Stanford Synchrotron Radiation Laboratory with a photon energy of 20 KeV. We collected diffraction patterns in the angle-dispersive mode using image plates; these patterns were angle-integrated to obtain the data shown here [J. H. Nguyen and R. Jeanloz, ibid. 64, 3456 (1993)]. In all cases the instrument resolution was far greater than the intrinsic diffraction linewidths because of the small crystallite size. We collected optical absorption spectra using a scanning ultraviolet-visible spectrometer with 2-nm resolution in 6 to 7 min. Optical transitions in wurtzite nanocrystals are electronically allowed, and the absorption consists of a series of discrete features in the visible region. Rock-salt nanocrystals have a band gap in the near-infrared, and the transitions are electronically forbidden but phonon-assisted, as in the bulk material [S. H. Tolbert, A. B. Herhold, C. S. Johnson, A. P. Alivisatos, Phys. Rev. Lett. 73, 3266 (1994)], resulting in a featureless absorption spectrum. We observed an abrupt change in the electronic absorption, a clear signature of the phase transition.
20. C. B. Murray, D. J. Norris, M. G. Bawendi, J. Am. Chem Soc. 115, 8706 (1993); J. E. B. Katari, V. L. Colvin, A. P. Alivisatos, J. Phys. Chem. 98, 4109 (1994).
21. C. B. Murray, D. J. Norris, M. G. Bawendi, J. Am. Chem Soc. 115, 8706 (1993); J. E. B. Katari, V. L. Colvin, A. P. Alivisatos, J. Phys. Chem. 98, 4109 (1994).
22. J. J. Shiang, A. V. Kadavanich, R. K. Grubbs, A. P. Alivisatos, J. Phys. Chem. 99, 17417 (1995).
23. 50 clusters form glasses between 1 and 2 GPa and behave as hydrostatic pressure media with gradients no greater than 0.5 GPa for the highest pressures obtained in these experiments.
24. N. Herron, J. C. Calabrese, W. E. Farneth, Y. Wang, Science 259, 1426 (1993).
25. A. L. Edwards and H. G. Drickamer, Phys. Rev. 122, 1149 (1961); W. C. Yu and P. J. Gielisse, Mater. Res. Bull. 6, 621 (1971).
26. A. L. Edwards and H. G. Drickamer, Phys. Rev. 122, 1149 (1961); W. C. Yu and P. J. Gielisse, Mater. Res. Bull. 6, 621 (1971).
27. A. Onodera, Rev. Phys. Chem. Jpn. 39, 65 (1969).
28. In calculating the barrier heights, we assumed that the variations in the thermodynamic transition point with size and temperature were small and could be neglected. The change in the thermodynamic transition point (72) is small compared to the full hysteresis width. The pressure dependence of the barrier heights will be discussed elsewhere (C.-C. Chen et al., in preparation).
29. The interface term most likely involves the breaking or rearrangement, or both, of bonds between surface atoms and organic capping ligands and depends on the types of ligands used.
30. E. C. Stoner and E. P. Wohlfarth, Philos. Trans. R. Soc. London Ser. A 240, 599 (1948); L. Néel, Ann. Geophys. 5, 99 (1949); D. D. Awschalom and D. P. DiVincenzo, Phys. Today 48, 43 (1995).
31. E. C. Stoner and E. P. Wohlfarth, Philos. Trans. R. Soc. London Ser. A 240, 599 (1948); L. Néel, Ann. Geophys. 5, 99 (1949); D. D. Awschalom and D. P. DiVincenzo, Phys. Today 48, 43 (1995).
32. E. C. Stoner and E. P. Wohlfarth, Philos. Trans. R. Soc. London Ser. A 240, 599 (1948); L. Néel, Ann. Geophys. 5, 99 (1949); D. D. Awschalom and D. P. DiVincenzo, Phys. Today 48, 43 (1995).
33. F. Bodker, S. Morup, S. Linderoth, Phys. Rev. Lett. 72, 282 (1994); J. P. Chen, C. M. Sorensen, K. J. Klabunde, G. C. Hadjipanayis, Phys. Rev. B 51, 11527 (1995).
34. F. Bodker, S. Morup, S. Linderoth, Phys. Rev. Lett. 72, 282 (1994); J. P. Chen, C. M. Sorensen, K. J. Klabunde, G. C. Hadjipanayis, Phys. Rev. B 51, 11527 (1995).
35. Y. Xie, Y. T. Qian, W. Z. Wang, S. Zhang, Y. Zhang, Science 272, 1926 (1996).
36. J. Lin, E. Cates, P. A. Bianooni, J. Am. Chem. Soc. 116, 4738 (1994).
37. H. Xia, O. Xia, A. L. Ruoff, Phys. Rev. B 47, 12925 (1993).
38. We thank A. Kadavanich, N. Mizumoto, X. Peng, and M. Schlamp for technical assistance with this project and R. Jeanloz and S. H. Tolbert for helpful discussions. Supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Material Science Division, of the U.S. Department of Energy (DOE) under contract DE-AC03-76F0098. In these experiments we used the facilities of the University of California-Lawrence Livermore National Laboratory Participating Research Team at the Stanford Synchrotron Radiation Laboratory, which is operated by the DOE, Division of Chemical Sciences.