HCl vapor-induced structural rearrangements of n-alkanoate self-assembled monolayers on ambient silver, copper, and aluminum surfaces

Journal of the American Chemical Society

Volumn 118, Issue 28, 1996, Pages 6724-6735

  Tao, Yu Tai ^a   Hietpas, Geoffrey D ^b   Allara, David L ^b  

^a INSTITUTE OF CHEMISTRY   (Taiwan)

^b PENNSYLVANIA STATE UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ALKANOIC ACID;

ARTICLE; DRUG BINDING; DRUG STRUCTURE; INFRARED SPECTROPHOTOMETRY; STRUCTURE ACTIVITY RELATION;

EID: 0029929196     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja960672i     Document Type: Article

References (59)

1. (a) Swalen, J. D.; Allara, D. L.; Andrade, J. D.; Chandross, E. A.; Garoff, S.; Israelachvili, J.; McCarthy, T. J.; Murry, R.; Pease, R. F.; Rabolt, J. F.; Wynne, K. J.; Yu, H. Langmuir 1987, 3, 932-950.
2. (b) For a general review, see: Ulman, A. An Introduction to Ultrathin Organic Films; Academic Press: Boston, 1991.
3. (c) Whitesides, G. M.; Ferguson, G. S.; Allara, D. L.; Scherson, D.; Speaker, L.; Ulman, A. Crit. Rev. Surf. Chem. 1993, 3, 49-65.
4. Laibinis, P. E.; Whitesides, G. M. J. Am. Chem. Soc. 1992, 114, 9022-9028.
5. Lercel, M. J.; Redinbo, G. F.; Pardo, M.; Rooks, M.; Tiberio, R. C.; Simpson, P.; Sheen, C. W.; Parikh, A. N.; Allara, D. L. J. Vac. Sci. Technol. 1994, B12, 3663-3667.
6. (a) Tarlov, M. J.; Burgess, D. R. F., Jr.; Gillen, G. J. Am. Chem. Soc. 1993, 115, 5305-5306.
7. (b) Huang, J.; Hemminger, J. C. J. Am. Chem. Soc. 1993, 115, 3342-3342.
8. Kumar, A.; Biebuyck, H. A.; Abbott, N. L.; Whitesides, G. M. J. Am. Chem. Soc. 1992, 114, 9188-9189.
9. (a) Allara, D. L.; Nuzzo, R. G. Langmuir 1985, 1, 45-52 and 52-65.
10. (b) Sondag, A. H. M.; Raas, M. C. J. Chem. Phys. 1989, 91, 4926-4931.
11. Schlotter, N. E.; Porter, M. D.; Bright, T. B.; Allara, D. L. Chem. Phys. Lett. 1986, 132, 93-98.
12. Tao, Y. T. J. Am. Chem. Soc. 1993, 115, 4350-4358.
13. Tao, Y. T.; Ma, L. F. J. Chin. Chem. Soc. 1994, 41, 481-485.
14. Laibinis, P. E.; Whitesides, G. M.; Allara, D. L.; Parikh, A.; Tao, Y. T.; Nuzzo, R. G. J. Am. Chem. Soc. 1991, 113, 7152.
15. Allara, D. L.; Parikh, A. N. J. Chem. Phys. 1992, 96, 927-945.
16. Maoz, R.; Sagiv, J. J. Colloid Interface Sci. 1984, 100, 465-496.
17. See refs 7 and 8 and: (a) Smith, E. L.; Porter, M. D. J. Phys. Chem. 1993, 97, 8032-8038. (b) Ahn, S. J.; Son, D. H.; Kim, K. J. Mol. Struct. 1994, 324, 223-231.
18. See refs 7 and 8 and: (a) Smith, E. L.; Porter, M. D. J. Phys. Chem. 1993, 97, 8032-8038. (b) Ahn, S. J.; Son, D. H.; Kim, K. J. Mol. Struct. 1994, 324, 223-231.
19. -/Ag interface cannot be accurately represented with analogous bulk carboxylate salts. In addition, we continually observe that the chain packing in n-alkanoate salts is poorer than in the corresponding SAMs, thus limiting the use of these salts as a source of accurate optical function values for simulation of SAM spectra. However, the spectra of the bulk long-chain acids in the C-H stretching region exhibit an extremely close match of frequencies and line widths to the corresponding SAMs. For this reason, the optical functions obtained from the bulk acids were used for quantitative simulations of the non-carboxyl features of the SAM spectra. Tabulated optical constant data of a number of the carboxylic acid and alkali metal salts are available from one of the authors (D.L.A.) on request.
20. Infrared band assignments for the C-H stretching modes of n-alkyl chains can be found in numerous references, e.g.: MacPhail, R. A.; Strauss, H. L.; Snyder, R. G.; Elliger, C. A. J. Phys. Chem. 1984, 88, 334-341. Previous assignments in SAMs can be found elsewhere, e.g., refs 6a, 7, 10, and 11.
21. Palik, E. D. Handbook of Optical Constants of Solids; Academic Press: New York, 1985; pp 353-357.
22. Such effects are prevalent in other SAM systems, e.g., n-alkanethiolates on Au (ref 10).
23. Samant, M. G.; Brown, C. B.; Gordon, J. G., II Langmuir 1993, 9, 1082-1085.
24. (a) Verma, A. R. Proc. R. Soc. A 1955, 228, 34-50.
25. (b) Sydow, E. V. Arkiv Kemi. 1956, 9, 231-254.
26. Hayashi, S.; Umemura, J. J. Chem. Phys. 1975, 63 (5), 1732-1740.
27. Bellamy, L. J. The Infrared Spectra of Complex Molecules; Wiley: New York, 1975.
28. Sinclair, R. G.; McKay, A. F.; Jones, R. N. J. Am. Chem. Soc. 1952, 74, 2570-2575.
29. Hill, I. R.; Levin, I. W. J. Chem. Phys. 1979, 70 (2), 842-851.
30. (a) Snyder, R. G.; Schachtschneider, J. H. Spectrochim. Acta. 1963, 19, 85-116.
31. (b) Sinclair, R. G.; McKay, A. F.; Jones, R. N. J. Am. Chem. Soc. 1952, 74, 2575-2578.
32. Snyder, R. G. J. Mol. Spectrosc. 1961, 7, 116-144.
33. Susi, H. J. Am. Chem. Soc. 1959, 81, 1535-1540.
34. 2 bending and rocking modes, respectively, are parallel to the a axis while the low frequency components are parallel to the b axis (refs 25 and 26), the relative doublet intensities will be determined by the a, b plane surface alignment. In the present example of the C16/Ag SAM spectrum taken after 10 s of HCl exposure (Figure 7) the high/low frequency mode intensity ratios for both the CH2 rocking and bending modes are ∼2.5:1. This result suggests that the a,b plane is oriented preferentially with the a axis away from the surface. However, without a knowledge of the intrinsic oscillator strengths this conclusion must be considered speculative.
35. Barr, M. R.; Dunell, B. A.; Grant, R. F. Can. J. Chem. 1963, 41, 1188-1196.
36. -1. [Hietpas, G. D.; Allara, D. L. Unpublished results.]
37. (a) Bruggeman, D. A. G. Ann. Phys.(Leipzig) 1935, 24, 636.
38. (b) Aspnes, D. E. Thin Solid Films 1982, 89, 249-262.
39. (c) Jellison, G. E., Jr. Thin Solid Films 1993, 234, 416-422.
40. We note that more rigorous treatments are available for calculations of the effective local electromagnetic field strengths in heterogeneous thin film media than the one used here [for example, see: Beaglehole, D. Mater. Res. Soc. Symp. Proc. 1995, 366, 77-88]. In general, deviations from the accuracy of EMA treatments based on uniform dielectric functions for the constituent materials in a thin heterogeneous slab will arise for films comprised of monolayers of particles on the size scale of ∼10 nm or less, with the exact deviations highly dependent on the size of the bulk dielectric function. However, since these deviations will primarily arise from the screening effects of in-plane (surface) polarization fields, they then will be neglible in the cases of highly metallic substrates, such as the present case, where the in-plane electric fields are near vanishing. For this reason, and also because of the overall uncertainty of the exact sizes of the crystallites and their distributions (see ref 33) the present level of calculations using standard EMA theory was selected as appropriate for the data analysis. More detailed approaches will be described elsewhere (see ref 32).
41. Hietpas, G.; Parikh, A.; Allara, D. Manuscript in preparation.
42. Attempts were made to verify the general size and surface distribution of these crystallites by atomic force microscopy (AFM). However, because of the inherent nm-scale roughness of the evaporated Ag substrates and the quality of the available instrumentation, it was not possible in these preliminary measurements to unambiguously identify what features were actually due to deposits of hexadecanoic acid. Further work with more carefully prepared substrates and improved instrumentation is in progress.
43. This angle was determined from the C form of stearic acid (ref 19b and references therein). This crystalline form (monoclinic symmetry with orthorhombic packing of the hydrocarbon chains) has been reported to be the only one formed for the even numbered fatty acids when rapidly crystallized from the melt or from solution. Accordingly, it is reasonable to assume that the rapid protonation and reorganization accompanying HCl exposure of the C16 SAM also results in this crystalline form.
44. Low, M. J. D.; Brown, K. H.; Inoue, H. J. J. Colloid Interface Sci. 1967, 24, 252-257.
45. Tompkins, H. G.; Allara, D. L. J. Colloid Interface Sci. 1974, 49, 410-421.
46. Gaines, G. L., Jr. J. Colloid. Sci. 1960, 15, 321.
47. Kasaoka, S.; Sakata, Y.; Shirata, M. Nippon Kagaku Kaishi 1977, 11, 1728-1736.
48. Bowker, M.; Waugh, K. C. Surf. Sci. 1983, 134, 639-664. Goddard, P. J.; Lambert, R. M. Surf. Sci. 1977, 67, 180-194. Schott, J. H.; White, H. S. J. Phys. Chem. 1994, 98, 291-296.
49. Bowker, M.; Waugh, K. C. Surf. Sci. 1983, 134, 639-664. Goddard, P. J.; Lambert, R. M. Surf. Sci. 1977, 67, 180-194. Schott, J. H.; White, H. S. J. Phys. Chem. 1994, 98, 291-296.
50. Bowker, M.; Waugh, K. C. Surf. Sci. 1983, 134, 639-664. Goddard, P. J.; Lambert, R. M. Surf. Sci. 1977, 67, 180-194. Schott, J. H.; White, H. S. J. Phys. Chem. 1994, 98, 291-296.
51. Graedel, T. E. J. Electrochem. Soc. 1992, 139, 1963-1970. Rice, D. W.; Peterson, P.; Rigby, E. B.; Phipps, P. B. P.; Cappell, R. J.; Tremoureux, R. J. Electrochem. Soc. 1981, 128, 275-284.
52. Graedel, T. E. J. Electrochem. Soc. 1992, 139, 1963-1970. Rice, D. W.; Peterson, P.; Rigby, E. B.; Phipps, P. B. P.; Cappell, R. J.; Tremoureux, R. J. Electrochem. Soc. 1981, 128, 275-284.
53. 3/2, 2p1/2, and 2s1/2 peaks were observed at 197.31, 198.92, and 268.36 eV, respectively, while the O1s peak was strongly diminished. Over the course of 3 days ambient exposure in a closed container, the C1 peaks were seen to decrease in intensity by a factor of ∼3 while the O core level peaks begin to reappear indicating reformation of the surface oxide.
54. Tao, Y. T. Unpublished Results.
55. -2 and thereby impart significant stability to several layers of alkyl chains into the crystallite. Since the experimental observations indicate near total conservation of material on the surface over many days it is clear that the crystallites are, in fact, quite stable. However, since it is not likely that this stability is due to kinetic factors, considering the extremely high surface/volume ratios of the crystallites, the above thermodynamic analysis suggests that the crystallite size distribution actually may be heavily skewed to favor larger sizes, close to the value of ∼5 nm derived from our IRS analysis. Growth of crystallites significantly larger than this size becomes diminishingly unlikely since the intercrystallite spacings will become huge on the molecular scale, a situation which would seem to conflict with the efficient surface diffusion required for the observed formation of C16 acid crystallites over periods of seconds during HCl exposure.
56. 2 and Ge by HCl [Saito, M.; Tabe, Y.; Saito, K.; Ikegami, K.; Kuroda, S.; Sugi, M. Jpn. J. Appl. Phys. 1990, 29 (10), 1892-1894] and on Si by HI [Pike, J. K.; Byrd, H.; Morrone, A. A.; Talham, D. R. J. Am. Chem. Soc. 1991, 115, 8497-8498], and reorganization of the hydrocarbon packing is observed in neither case.
57. 2 and Ge by HCl [Saito, M.; Tabe, Y.; Saito, K.; Ikegami, K.; Kuroda, S.; Sugi, M. Jpn. J. Appl. Phys. 1990, 29 (10), 1892-1894] and on Si by HI [Pike, J. K.; Byrd, H.; Morrone, A. A.; Talham, D. R. J. Am. Chem. Soc. 1991, 115, 8497-8498], and reorganization of the hydrocarbon packing is observed in neither case.
58. 2 and Ge by HCl [Saito, M.; Tabe, Y.; Saito, K.; Ikegami, K.; Kuroda, S.; Sugi, M. Jpn. J. Appl. Phys. 1990, 29 (10), 1892-1894] and on Si by HI [Pike, J. K.; Byrd, H.; Morrone, A. A.; Talham, D. R. J. Am. Chem. Soc. 1991, 115, 8497-8498], and reorganization of the hydrocarbon packing is observed in neither case.
59. -1 can be observed in the IRS spectrum over this time scale.