Two-dimensional melting of an anisotropic crystal observed at the molecular level

Science

Volumn 278, Issue 5343, 1997, Pages 1604-1607

  Sikes, H D ^a   Schwartz, D K ^a  

^a Tulane University   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ANISOTROPY; ATOMIC FORCE MICROSCOPY; CHARACTERIZATION; CRYSTALS; DISLOCATIONS (CRYSTALS); INFRARED SPECTROSCOPY; LANGMUIR BLODGETT FILMS; MELTING; SMECTIC LIQUID CRYSTALS;

HEXATIC PHASE; MOLECULAR PERIODICITY; ORTHORHOMBIC CRYSTAL PHASE; TWO DIMENSIONAL MELTING TRANSITION;

PHASE TRANSITIONS;

ANISOTROPY; ARTICLE; CRYSTAL STRUCTURE; INFRARED SPECTROSCOPY; OBSERVATION; OPTICAL RESOLUTION; PERIODICITY; PRIORITY JOURNAL; SPECTRAL SENSITIVITY;

EID: 1842331539     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.278.5343.1604     Document Type: Article

References (30)

1. D. R. Nelson, Phys. Rev. B 18, 2318 (1978); B. I. Halperin and D. R. Nelson, Phys. Rev. Lett. 41, 121 (1978); D. R. Nelson and B. I. Halperin, Phys. Rev. B 19, 2457 (1979); A. P. Young, ibid., p. 1855.
2. D. R. Nelson, Phys. Rev. B 18, 2318 (1978); B. I. Halperin and D. R. Nelson, Phys. Rev. Lett. 41, 121 (1978); D. R. Nelson and B. I. Halperin, Phys. Rev. B 19, 2457 (1979); A. P. Young, ibid., p. 1855.
3. D. R. Nelson, Phys. Rev. B 18, 2318 (1978); B. I. Halperin and D. R. Nelson, Phys. Rev. Lett. 41, 121 (1978); D. R. Nelson and B. I. Halperin, Phys. Rev. B 19, 2457 (1979); A. P. Young, ibid., p. 1855.
4. D. R. Nelson, Phys. Rev. B 18, 2318 (1978); B. I. Halperin and D. R. Nelson, Phys. Rev. Lett. 41, 121 (1978); D. R. Nelson and B. I. Halperin, Phys. Rev. B 19, 2457 (1979); A. P. Young, ibid., p. 1855.
5. J. M. Kosterlitz and D. J. Thouless, J. Phys. C 6, 1181 (1973).
6. C. A. Murray, W. A. Sprenger, R. A. Wenk, Phys. Rev. B 42, 688 (1990).
7. P. S. Pershan, Structure of Liquid Crystal Phases. (World Scientific, Singapore, 1988).
8. C. M. Knobler and R. C. Desai, Annu. Rev. Phys. Chem. 43, 207 (1992).
9. S. Garoff, H. W. Deckman, J. H. Dunsmuir, M. S. Alvarez, J. Phys. (Paris) 47, 701 (1986); R. Viswanathan, L. L. Madsen, J. A. Zasadzinski, D. K. Schwartz, Science 269, 51 (1995).
10. S. Garoff, H. W. Deckman, J. H. Dunsmuir, M. S. Alvarez, J. Phys. (Paris) 47, 701 (1986); R. Viswanathan, L. L. Madsen, J. A. Zasadzinski, D. K. Schwartz, Science 269, 51 (1995).
11. S. Ostlund and B. I. Halperin, Phys. Rev. B 23, 335 (1981).
12. J. P. Rabe, J. D. Swalen, J. F. Rabolt, J. Chem. Phys. 86, 1601 (1987); L. Rothberg, G. S. Higashi, D. L. Allara, S. Garoff, Chem. Phys. Lett. 133, 67 (1987); T. Hasegawa, S. Takeda, A. Kawaguchi, J. Umemura, Langmuir 11, 1236 (1995).
13. J. P. Rabe, J. D. Swalen, J. F. Rabolt, J. Chem. Phys. 86, 1601 (1987); L. Rothberg, G. S. Higashi, D. L. Allara, S. Garoff, Chem. Phys. Lett. 133, 67 (1987); T. Hasegawa, S. Takeda, A. Kawaguchi, J. Umemura, Langmuir 11, 1236 (1995).
14. J. P. Rabe, J. D. Swalen, J. F. Rabolt, J. Chem. Phys. 86, 1601 (1987); L. Rothberg, G. S. Higashi, D. L. Allara, S. Garoff, Chem. Phys. Lett. 133, 67 (1987); T. Hasegawa, S. Takeda, A. Kawaguchi, J. Umemura, Langmuir 11, 1236 (1995).
15. M. Shimomura, K. Song, J. P. Rabolt, Langmuir 8, 887 (1992).
16. C. Böhm, R. Steitz, H. Riegler, Thin Solid Films 178, 511 (1989).
17. M. R. Buhaenko, M. J. Grundy, R. M. Richardson, S. J. Roser, ibid. 159, 253 (1988); Y. Sasanuma, Y. Kitano, A. Ishitani, H. Nakahara, K. Fukuda, ibid. 199, 359 (1991).
18. M. R. Buhaenko, M. J. Grundy, R. M. Richardson, S. J. Roser, ibid. 159, 253 (1988); Y. Sasanuma, Y. Kitano, A. Ishitani, H. Nakahara, K. Fukuda, ibid. 199, 359 (1991).
19. P. Tippmann-Krayer, R. M. Kenn, H. Möhwald, ibid. 210/211, 577 (1992).
20. D. K. Schwartz, J. Garnaes, R. Viswanathan, J. A. N. Zasadzinski, Science 257, 508 (1992); D. K. Schwartz, J. Garnaes, R. Viswanathan, S. Chiruvolu, J. A. N. Zasadzinski, Phys. Rev. E 47, 452 (1993).
21. D. K. Schwartz, J. Garnaes, R. Viswanathan, J. A. N. Zasadzinski, Science 257, 508 (1992); D. K. Schwartz, J. Garnaes, R. Viswanathan, S. Chiruvolu, J. A. N. Zasadzinski, Phys. Rev. E 47, 452 (1993).
22. J. Garnaes, D. K. Schwartz, R. Viswanathan, J. A. N. Zasadzinski, Nature 357, 54 (1992).
23. 2 subphase (Millipore water was used), adjusted to pH = 6.5, and contained in a Nima (Coventry, England) LB trough. Imaging was performed with the use of a Nanoscope III Multimode atomic force microscope (Digital Instruments) in contact mode using a silicon nitride cantilever with integral tip. The equilibrium deflection of a given cantilever was quite sensitive to temperature; therefore, the tip was withdrawn before large temperature jumps and re-engaged after the temperature had stabilized. A small thermoelectric Peltier element (Melcor, Trenton, NJ) and a thermocouple (Omega Engineering, Stanford, CT) were sandwiched between a magnetic stainless steel base and a small piece of copper sheet and bonded together with thermally conductive epoxy. The entire assembly was less than 5 mm thick and 12 mm in cross section. Extremely thin and flexible electrical leads were carefully strain-relieved to avoid transmission of vibrations to the microscope. Over the usable temperature range of the device, 20° to 120°C, the scanner temperature remained below 35°C, minimizing difficulties associated with thermal drift. A previously reported temperature-controlled microstage (16) functioned only below 80°C. Several important control experiments were performed to validate the technique. Invariant molecular-resolution images of mica substrates were obtained to well above 100°C. High-resolution images of all three types of structure were quantitatively consistent after changing the scan size or rate, rotating the scan direction, or annealing at constant temperature for hours. The surface structure changed at the same temperature in nine separate repetitions of the experiment (using different samples and AFM tips) and reversibly changed back upon lowering of the temperature while using the same tip. On one occasion, we were even able to maintain the tip in contact with the film during this thermal cycling and continuously observed the loss and then reappearance of molecular order. These experiments prove that the loss of molecular resolution was due to increased molecular disorder, not degradation of a particular tip, and that the images represent structure indigenous to the sample, not related to temporal noise or induced by scanning.
24. I. Musevic, G. Slak, R. Blinc, Rev. Sci. Instrum. 67, 2554 (1996).
25. J. Toner and D. R. Nelson, Phys. Rev. B 23, 316 (1981).
26. J. Y. Josefowicz et al., Science 260, 323 (1993).
27. D. G. Cameron and R. A. Dluhy, in Spectroscopy in the Biomedical Sciences, R. M. Gendreau, Ed. (CRC Press, Boca Raton, FL, 1986), pp. 53-86.
28. Transmission IR spectra were recorded with the use of a Mattson Cygnus 100 spectrometer with a 6.4-mm pinhole defining the incident beam. The sample holder was heated using a thin film resistive heating element (Minco, Minneapolis, MN); the temperature was measured with a thermocouple (Omega). After obtaining the multilayer spectrum, the sample holder was removed and placed in an ultraviolet-oxygen cleaner (Boekel Industries, Feasterville, PA), where the film on both sides of the substrate was removed. The holder was then repositioned within the spectrometer, to within 0.1 mm of the original position, and the background spectrum was measured.
29. C.-Y. Chao, C.-F. Chou, J. T. Ho, A. Jin, C. C. Huang, Phys. Rev. Lett. 77, 2750 (1996).
30. We thank D. R. Nelson for his helpful comments regarding 2D melting. This work was supported by the National Science Foundation (NSF), the donors of the Petroleum Research Fund, and the Center for Photoinduced Processes (funded by NSF and the Louisiana Board of Regents).