pubs.acs.org/Langmuir © 2009 American Chemical Society
In Situ Crystallized Zirconium Phenylphosphonate Films with Crystals Vertically to the Substrate and Their Hydrophobic, Dielectric, and Anticorrosion Properties Zhaohui Cui, Fazhi Zhang,* Lei Wang, Sailong Xu, and Xiaoxiao Guo State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Box 98, Beijing 100029, China Received June 3, 2009. Revised Manuscript Received July 19, 2009 The in situ crystallization technique has been utilized to fabricate zirconium phenylphosphonate (ZrPP) films with their hexagonal crystallite perpendicular to the copper substrate. The micro/nano roughness surface structure, as well as the intrinsic hydrophobic characteristic of the surface functional groups, affords ZrPP films excellent hydrophobicity with water contact angle (CA) ranging from 134° to 151°, without any low-surface-energy modification. Particularly, in the corrosive solutions such as acidic or basic solutions over a wide pH from 2 to 12, no obvious fluctuation in CA was observed for all the ZrPP film. The k values of the hydrophobic ZrPP films are in the low-k range (k < 3.0), meeting the development of ultra-large-scale integration (ULSI) circuits. The hydrophobicity feature is proposed to bear ZrPP film a more stable low-k value in an ambient atmosphere. Besides, the polarization current of ZrPP films is reduced by 2 orders of magnitude, compared to that of the untreated copper substrate. Even deposited in a vacuum oven for 30 days at room temperature, ZrPP films also show excellent corrosion resistance, indicating a stable anticorrosion property.
Introduction Layered metal(IV) phosphates and phosphonates have attracted much attention for their potential application as catalysts, ion-exchangers, intercalating agents, solid state gas sensors, proton conduction, and substrates for the immobilization of biological materials.1 Among the metal phosphates and phosphonates, zirconium phosphates and phosphonates were given special attention. It is believed that oriented films have attracted great attention in transistors, devices, microchips, proton conduction, and other areas for their peculiar property superior to the random oriented films and powder.2 For the purpose of developing novel applications of zirconium phosphates and phosphonates as innovative film or device materials, intensive studies have been conducted with the aim of organizing the microcrystals into large, uniformly aligned 2D arrays. Oriented zirconium phosphate and derivatives films with hexagonal crystallites oriented parallel to the substrate surface have been prepared by spincoating3a and anodic electrodeposition,3b owing to the intrinsic *Corresponding author. E-mail:
[email protected]. (1) (a) Troup, J. M.; Clearfield, A. Inorg. Chem. 1977, 16, 3311. (b) Alberti, G.; Costantino, U.; Alluli, S.; Tomassini, N. J. Inorg. Nucl. Chem. 1978, 40, 1113. (c) Katz, H. E.; Scheller, G.; Putvinski, T. M.; Schiling, M. L.; Wilson, W. L.; Chidsey, C. E. D. Science 1991, 254, 1485. (d) Shpeizer, B.; Poojary, D. M.; Ahn, K.; Runyan, C. E.; Clearfield, A. Science 1994, 266, 1357. (e) Alberti, G.; Casciola, M.; Costantino, U.; Vivani, R. Adv. Mater. 1996, 8, 291. (f) Curini, M.; Montanari, F.; Rosati, O.; Lioy, E.; Margarita, R. Tetrahedron Lett. 2003, 44, 3923. (g) Subbiah, A.; Pyle, D.; Rowland, A.; Huang, J.; Narayanan, R. A.; Thiyagarajan, P.; Zon, J.; Clearfield, A. J. Am. Chem. Soc. 2005, 127, 10826. (2) (a) Law, M.; Greene, L. E.; Johnson, J. C.; Saykally, R.; Yang, P. D. Nat. Mater. 2005, 4, 455. (b) Lai, Z. P.; Bonilla, G.; Diaz, I.; Nery, J. G.; Sujaoti, K.; Amat, M. A.; Kokkoli, E.; Terasaki, O.; Thompson, R. W.; Tsapatsis, M.; Vlachos, D. G. Science 2003, 300, 456. (c) Lee, H. N.; Hesse, D.; Zakharov, N.; G€osele, U. Science 2002, 296, 2006. (d) Shibata, T.; Fukuda, K.; Ebina, Y.; Kogure, T.; Sasaki, T. Adv. Mater. 2008, 20, 231. (e) Kim, H. S.; Pham, T. T.; Yoon, K. B. J. Am. Chem. Soc. 2008, 130, 2134. (f) Zhu, K.; Vinzant, T. B.; Neale, N. R.; Frank, A. J. Nano Lett. 2007, 7, 3739. (g) Yu, H. D.; Zhang, Z. P.; Han, M. Y.; Hao, X. T.; Zhu, F. R. J. Am. Chem. Soc. 2005, 127, 2378. (3) (a) Nishiyama, Y.; Tanaka, S.; Hillhouse, H. W.; Nishiyama, N.; Egashira, Y.; Ueyama, K. Langmuir 2006, 22, 9469. (b) Takei, T.; Kobayashi, Y.; Hata, H.; Yonesaki, Y.; Kumada, N.; Kinomura, N.; Mallouk, T. E. J. Am. Chem. Soc. 2006, 128, 16634.
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propensity of the crystallites to align in an orientation that leads to maximum face-to-face contact between the crystallites and the substrate. To the best of our knowledge, there are no reports about the preparation and properties of the oriented zirconium phosphates and phosphonates films with crystallites perpendicular to the substrate surface. Recently, in situ crystallization was developed by our group for the preparation of an oriented anionic clay-layered double hydroxides (LDHs, whose structure is based on brucite (Mg(OH)2)-like layers) film on the surface of anodized alumina or polystyrene substrates.4 The LDHs film is extremely well oriented with crystallites ab face vertical to the substrate surface, and the good adhesion between the film and underlying substrate is important for practical purposes. The multiscaled micro/nano structures of the film surface can be controlled by tuning crystallization temperature and time. After a simple surface modification with inexpensive surfactants, the film showed excellent superhydrophobicity.4a A laurate anion intercalated ZnAl-LDHs film with superhydrophobicity was also synthesized using the same protocol.4b In recent years, superhydrophobic surfaces5 have attracted considerable research interest because of their significant potential practical applications including transparent and antireflective superhydrophobic coatings in architecture or automobile windows, eyeglasses, optical windows for electronic devices, superhydrophobic coating with structural colors in the external decoration of architectures, fluidic drag reduction, (4) (a) Chen, H. Y.; Zhang, F. Z.; Fu, S. S.; Duan, X. Adv. Mater. 2006, 18, 3089. (b) Zhang, F. Z.; Zhao, L. L.; Chen, H. Y.; Xu, S. L.; Evans, D. G.; Duan, X. Angew. Chem., Int. Ed. 2008, 47, 2466. (c) L€u, Z.; Zhang, F. Z.; Lei, X. D.; Yang, L.; Evans, D. G.; Duan, X. Chem. Eng. Sci. 2007, 62, 6069. (d) L€u, Z.; Zhang, F. Z.; Lei, X. D.; Yang, L.; Xu, S. L.; Duan, X. Chem. Eng. Sci. 2008, 63, 4055. (5) (a) Feng, L.; Li, S.; Li, Y.; Li, H.; Zhang, L.; Zhai, J.; Song, Y.; Liu, B.; Jiang, L.; Zhu, D. Adv. Mater. 2002, 14, 1857. (b) Roach, P.; Shirtcliffe, N. J.; Newton, M. I. Soft Matter 2008, 4, 224. (c) Cheng, Z. J.; Feng, L.; Jiang, L. Adv. Funct. Mater. 2008, 18, 3219. (d) Sun, T. L.; Tan, H.; Han, D.; Fu, Q.; Jiang, L. Small 2005, 1, 959. (e) Chen, W.; Fadeev, A. Y.; Hsieh, M. C.; Oner, D.; Youngblood, J.; McCarthy, T. J. Langmuir 1999, 15, 3395. (f) Jiang, Y. G.; Wan, P. B.; Smet, M.; Wang, Z. Q.; Zhang, X. Adv. Mater. 2008, 20, 1972. (g) Wang, S. T.; Feng, L.; Jiang, L. Adv. Mater. 2006, 18, 767.
Published on Web 08/03/2009
DOI: 10.1021/la901981y
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enhancing water supporting force, controlled transportation of fluids, antibiofouling, prevention of water corrosion, oil/water separation, microcondensation, etc.6 The above studies show that superhydrophobic coatings are used to not only improve the performance of conventional materials by surface modification but also bring about new functions which are not available for the materials themselves. In the present work, we utilize the organic functionalization of zirconium phosphonates to facilely fabricate a film material with an improved hydrophobicity. In particular, we prepare zirconium phenylphosphonate (ZrPP, Zr(C6H5PO3)2 3 nH2O) film with crystals vertically to the substrate by in situ crystallization. The micro/ nano roughness surface structure, as well as the intrinsic hydrophobic characteristic of the surface functional groups, affords ZrPP film excellent hydrophobicity without any low-surfaceenergy modification. The one-step fabrication of ZrPP film is capable of facile preparation of superhydrophobic surfaces with large scale and good homogeneity. Considering the development of new potential functions for the hydrophobic materials, especially in the field of microelectronic device, the dielectric property and the corrosion resistance as well as the hydrophobicity of the ZrPP film were evaluated. Metal copper substrate, due to its lower bulk electrical resistivity and improved electromigration endurance, was adopted here for the coincidence with the demand of the microelectronic devices.
Experimental Section Synthesis of ZrPP Film. The ZrPP film was prepared by in situ crystallization on copper substrate (Shanghai Jing Xi Chemical Technology Co., Ltd., purity >99.5%, thickness 0.08 mm). Concentrated hydrofluoric acid and ZrOCl2 3 8H2O were added to 0.02 M phenylphosphonic acid (C6H5PO(OH)2, Aldrich) solution in such an amount as to reach the ratios [C6H5PO(OH)2]/[Zr] = 2 and [F]/[Zr] = 6. The copper substrate was then placed in the above solution in a Teflon-lined stainless steel autoclave which was placed in a conventional oven at 100 or 120 °C for the crystallization time from 0.5 to 24 h. After completion of the ZrPP film growth, the substrate was taken out of the autoclave, rinsed with ethanol, and dried at room temperature. Characterization. Powder X-ray diffraction (XRD) data were collected on a Rigaku XRD-6000 powder diffractometer, using Cu KR radiation (40 kV, 30 mA, and λ = 1.542 A˚) between 3° and 60° with a scanning rate of 10°/min. Scanning electron microscopy (SEM) was carried out on a Hitachi S-4700N instrument. The accelerating voltage applied was 20 kV. All the samples were sputtered with gold. Static water contact angles were measured with a commercial system for drop-shape analysis (DSA 100, KR€ uSS GmbH, Germany) at ambient temperature. The equilibrium water contact angle was measured with a fixed needle supplying a water drop while the drop-shape analysis system determined the contact angle. Three different points on each sample were investigated, and the average value was determined. Precise pH values were measured using DELTA 320 pH meters at ambient temperature. Polarization curves were obtained by using a Cypress Systems CS-300 potentiostat at room temperature. A three-electrode configuration was employed in the circuit with the sample as working electrode, a platinum counter electrode, and a saturated calomel electrode as reference electrode. An 3.5% aqueous solution of sodium chloride was used as electrolyte. The sweep rate was set at 10 mV s-1. Samples were immersed in a corrosive medium (3.5% aqueous sodium chloride solution) for 30 min before the test.
(6) Zhang, X.; Shi, F.; Niu, J.; Jiang, Y. G.; Wang, Z. Q. J. Mater. Chem. 2008, 18, 621.
180 DOI: 10.1021/la901981y
Figure 1. XRD patterns of the ZrPP film crystallized at 100 °C for 1 h (a), the ZrPP powder scraped from the film (b), and the copper substrate (c), with “/” indicating peaks from the copper substrate. The dielectric constant was measured by an Agilent 4294A impedance analyzer. A metal-insulator-metal (MIM) capacitor structure was fabricated. The sample was first cut to a size of 1 1 cm. The backsides of the coated copper substrate were scratched. On the top film side, silver paste was deposited to form an electrode. The dielectric constant of the ZrPP films was calculated by measuring the capacitance of the MIM structure at a frequency of 1 MHz on the Agilent 4294A impedance analyzer. The prepared samples were all dried overnight at 100 °C followed by cooling in desiccator prior to the capacitance measurement to minimize water adsorption. The capacitance was measured in several areas of the sample, and the k value reported here is an average. The adhesion of the ZrPP film on the substrate was performed according to the method reported in the previous literature.7
Results and Discussion Figure 1 illustrates the XRD patterns of the as-prepared ZrPP film and the corresponding ZrPP powder scraped from the film and the copper substrate. A low-angle reflection at 5.89° of the ZrPP powder was observed in Figure 1b, corresponding to the (002) reflections of ZrPP phase with a basal interlayer spacing of 14.6 A˚.8a The XRD pattern of the ZrPP film (Figure 1a) shows several basal (00l) and nonbasal (hkl) reflections, essentially identical to that of the ZrPP powder. The FT-IR spectrum of the ZrPP powder was observed in Figure 2. The sharp medium intensity band at 1439 cm-1 is probably the CdC stretch of the phenyl ring, and the 748 and 692 cm-1 bands are assigned to the absorptions of C-P bonds in the framework structure. The above results are consistent with the FT-IR spectrum of the powder ZrPP reported in the literature.8b The XRD and FT-IR results demonstrate the successful formation of a ZrPP film on the copper substrate. Figure 3 shows the SEM images of the ZrPP films crystallized at 100 °C for different crystallization times. After 0.5 h of crystallization, the curved hexagonal faces, perpendicular to the substrate, of the ZrPP microcrystals can be clearly observed. The ZrPP microcrystals cover almost the entire substrate surface (Figure 3a). The surface of film displays a nestlike roughness (7) (a) Beving, D. E.; McDonnell, A. M. P.; Yang, W. S.; Yan, Y. S. J. Electrochem. Soc. 2006, 153, B325. (b) Zhang, F. Z.; Sun, M.; Xu, L. S.; Zhao, L. L.; Zhang, B. W. Chem. Eng. J. 2008, 141, 362. (8) (a) Poojary, M. D.; Hu, H. L.; Campbell, F. L.; Clearfield, A. Acta Crystallogr. 1993, B49, 996. (b) Stein, E. W.; Clearfield, A.; Subramanian, M. A. Solid State Ionics 1996, 83, 113.
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Figure 2. FT-IR spectrum of the ZrPP powder scraped from the film.
microstructure morphology composed of 5-10 nm thick interlaced plates. Upon prolonging in the crystallization time from 0.5 to 6 h, a growth in thickness of the ZrPP plates was obviously found (Figure 3b,c), leading to less pores among the nanosheets. When the crystallization time reached 24 h, a compact and continuous morphology was obtained, as shown in Figure 3d. The cross-section view of SEM images (Figure 3e-h) clearly demonstrates the ZrPP platelets are perpendicular to the substrate, according to the “evolutionary selection” mechanism, first proposed by Van der Drift to explain the preferred orientation of a vapor-deposited PbO layer.9 In the early growth stages, crystal seeds begin to grow in all possible directions, but if the growth rates along different crystallographic axes are not the same, then the direction with the fastest growth rate makes a different angle to the normal to the surface for each crystal. When two crystals meet, the less steeply growing crystal is prevented from further growth by the more steeply growing crystal, which continues to grow. Repetition of this process ensures that crystals with their fastest growth direction normal to the substrate eventually envelop all the other crystals and finally dominate the film. For the anisotropic platelet ZrPP crystallites, growth in the ab-direction is obviously faster than that in the c-direction, and thus the film becomes dominated by crystallites growing with their ab-planes perpendicular to the substrate. Besides, we can see that a monolayer of the ZrPP crystals with a thickness of about 1.8 μm was grown on the copper substrate crystallized at 100 °C for 1 h (Figure 3f), and the film thickness increased to about 4.5 μm for 6 h crystallization (Figure 3g). Similar surface morphology was obtained with increasing crystallization temperature from 100 to 120 °C. The surface wettability of the ZrPP thin films was investigated by water contact angle (CA) measurements. An image of a water droplet on the as-synthesized ZrPP film is exhibited in Figure 3b (inset). The CA of the ZrPP film crystallized at 100 °C for 1 h was measured to be about 143°, indicating that the surface wettability of the ZrPP thin films are hydrophobic without low-surfaceenergy modification. The in situ crystallization herein shows to be an effective approach for the one-step fabrication of excellent hydrophobic surfaces of large scale and good homogeneity. The CA of other ZrPP films crystallized for different periods are shown in Table 1. The wettability of a surface is generally considered to depend on both its chemical nature and topology.4 (9) Drift, A. van der Philips Res. Rep. 1967, 22, 267.
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Article
In our case, the intrinsic hydrophoic terminal phenyl groups on the surface together with the fabrication of the nestlike microstructures favor the excellent hydrophobicity of the ZrPP film. Partically, in the corrosive solutions such as acidic or basic solutions over a wide pH from 2 to 12, no obvious fluctuation in CA was observed for all the ZrPP films, indicating that pH has no effect on the hydrophobicity of the ZrPP film. The above results indicate that the ZrPP film has a stable hydrophobicity, not only in pure water but also in corrosive acids and bases, which is very important for expanding its application. This hydrophobicity improvement is expected to decrease the moisture adsorption and thus help stabilize the k value of the lowk materials in an ambient atmosphere. In the recent years, there is a need for new low-k materials to replace the conventional silicon dioxide (k = 3.9-4.2) as an interlayer dielectric for the future microelectronic devices.10 A number of promising candidate materials have been investigated, including organic polymers such as the highly fluorinated alkane derivatives11 and porous inorganic materials such as the random or oriented porous inorganic silica12 and the porous pure-silica zeolites (PSZs).13 However, the hydroxyl groups in the surface of the inorganic materials, resulting in hydrophilic surface, are believed to an increase of k value drastically and a possibility of corrosion.14 Thus, it is important to make the porous inorganic material more hydrophobic so that it is less influenced by water vapor adsorption. Vapor phase silylation treatment of the as-synthesized zeolite film using chlorotrimethylsilane,15 as well as the organic functionalization of zeolite crystals during the synthesis of a zeolite nanoparticle suspension by adding methyltrimethoxysilane into the synthesis solution,16 has been adopted understandably for improving hydrophobicity and achieving a more stable k value in an ambient atmosphere. Standard test results of k value of ZrPP films prepared with varying the preparation conditions are shown in Table 1. The k value of ZrPP films is indeed in the low-k range (k < 3.0) meeting the development of ultra-largescale integration circuits. The hydrophobicity feature is proposed to bear ZrPP film a more stable low-k value in an ambient atmosphere. Metal copper is commonly used in the microelectronics industry destined to replace aluminum and its alloys. Despite the valuable properties of copper, its susceptibility to corrosion, in particular, the formation of nonvolatile compounds upon (10) (a) Miller, R. D. Science 1999, 286, 421. (b) Hatton, B. D.; Landskron, K.; Hunks, W. J.; Bennett, M. R.; Shukaris, D.; Perovic, D. D.; Ozin, G. A. Mater. Today 2006, 9, 22. (c) Treichel, H.; Goonetilleke, C. Adv. Eng. Mater. 2001, 3, 461. (d) Maex, K.; Baklanov, M. R.; Shamiryan, D.; Iacopi, F.; Brongersma, S. H.; Yanovitskaya, Z. S. J. Appl. Phys. 2003, 93, 8793. (11) (a) Rosenmeyer, C. T.; Wu, H. Proc. Mater. Res. Soc. 1996, 427, 463. (b) Rosenmeyer, C. T.; Bartz, J. W.; Hammes, J. Proc. Mater. Res. Soc. 1997, 476, 231. (12) (a) Lu, Y.; Ganguli, R.; Drewien, C. A.; Anderson, M. T.; Brinker, C. J.; Gong, W.; Guo, Y.; Soyez, H.; Dunn, B.; Huang, M. H.; Zink, J. I. Nature 1997, 389, 364. (b) Zhao, D. Y.; Feng, J. I.; Huo, Q. S.; Melosh, N.; Fredrickson, G. H.; Chmelka, B. F.; Stucky, G. D. Science 1998, 279, 548. (c) Pai, R. A.; Humayun, R.; Schulberg, M. T.; Sengupta, A.; Sun, J. N.; Watkins, J. J. Science 2004, 303, 507. (13) (a) Li, Z. J.; Johnson, M. C.; Sun, M. W.; Ryan, E. T.; Earl, D. J.; Maichen, W.; Martin, J. I.; Li, S.; Lew, C. M.; Wang, J. L.; Deem, M. W.; Davis, M. E.; Yan, Y. S. Angew. Chem., Int. Ed. 2006, 45, 6329. (b) Li, S.; Li, Z. J.; Medina, D.; Lew, C.; Yan, Y. S. Chem. Mater. 2005, 17, 1851. (c) Li, S.; Li, Z. J.; Yan, Y. S. Adv. Mater. 2003, 15, 1528. (d) Wang, Z. B.; Wang, H. T.; Mitra, A.; Huang, L. M.; Yan, Y. S. Adv. Mater. 2001, 13, 746. (14) Maex, K.; Baklanov, M. R.; Shamiryan, D.; Lacopi, F.; Brongersma, S. H.; Yanovitskaya, Z. S. J. Appl. Phys. 2003, 93, 8793. (15) (a) Li, Z. J.; Li, S.; Luo, H. M.; Yan, Y. S. Adv. Funct. Mater. 2004, 14, 1019. (b) Wang, Z. B.; Mitra, A.; Wang, H. T.; Huang, L. M.; Yan, Y. S. Adv. Mater. 2001, 13, 1463. (16) (a) Eslava, S.; Iacopi, F.; Baklanov, M. R.; Kirschhock, C. E. A.; Maex, K.; Martens, J. A. J. Am. Chem. Soc. 2007, 129, 9288. (b) Eslava, S.; Baklanov, M. R.; Neimark, A. V.; Iacopi, F.; Kirschhock, C. E. A.; Maex, K.; Martens, J. A. Adv. Mater. 2008, 20, 3110. (c) Eslava, S.; Kirschhock, C. E. A.; Aldea, S.; Baklanov, M. R.; Iacopi, F.; Maex, K.; Martens, J. A. Microporous Mesoporous Mater. 2009, 118, 458.
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Figure 3. Top and cross-section views of SEM images of the ZrPP films crystallized at 100 °C for different times: (a, e) 0.5 h, (b, f) 1 h, (c, g) 6 h, and (d, h) 24 h. Table 1. Water Contact Angle and k Value of the ZrPP Films Obtained at Different Crystallization Temperatures and Times
samples
crystallization temperature [°C ]
crystallization time [h]
water contact angle [deg]a
k value
1-a 1-b 1-c 1-d 2-a 2-b 2-c
100 0.5 138/130/129 100 1 143/140/140 2.27 ( 0.07 100 6 134/130/131 2.43 ( 0.02 100 24 141/140/139 120 0.5 140/139/139 120 1 151/150/151 2.74 ( 0.05 120 6 143/141/141 2.95 ( 0.02 a The water contact angle was measured by placing a water droplet with the different pH on top of the film: pH = 7/pH = 2/pH = 12.
Figure 4. Polarization curves (vs SCE) of samples immersed in 3.5% aqueous sodium chloride solution at room temperature for 30 min: (a) bare copper substrate, (b) ZrPP film, and (c) ZrPP film after deposited in a vacuum oven for 30 days at room temperature.
reaction with common etching processes (chlorine- or fluorinebased) and atmospheric oxidation is concerned.17 Our group have shown that a laurate anion intercalated-ZnAl-LDHs film with superhydrophobicity provides long-term corrosion protection of the coated aluminum substrate and provides an effective barrier to aggressive species.4b The corrosion resistance of ZrPP films was investigated by dc polarization; the lower the polarization current, the better the corrosion resistance. After coating the hydrophobic ZrPP film, the polarization current is reduced by 2 orders of magnitude (Figure 4b), compared to that of the untreated copper substrate. Even deposited in a vacuum oven for 30 days at room temperature, hydrophobic ZrPP film also shows excellent corrosion resistance, indicating a stable anticorrosion property (Figure 4c). (17) Whelan, C. M.; Kinsella, M.; Ho, H. M.; Maex, K. J. Electrochem. Soc. 2004, 151, B33.
182 DOI: 10.1021/la901981y
Figure 5. SEM image of ZrPP film on copper substrate tested for adhesion.
Strong adhesion of the dielectric coatings as well as corrosion resistance to the metal surface is of critical importance. Void space at the coating-metal interface is responsible for the accumulation of water and ions at the interface and believed to be a primary failure mechanism for corrosion resistant coatings. Figure 5 shows the SEM result of the adhesion of ZrPP film on the surface of copper substrate analyzed according to the method reported previously.7 There was no significant peeling off of film after the cross cutting through the ZrPP film, indicating a strong adhesion between the copper substrate and ZrPP coating.
Conclusions The ZrPP films with their crystallite ab-face perpendicular to the copper substrate were fabricated by the in situ crystallization technique. The nestlike microstructure of the ZrPP film surface can be tailored by varying crystallization temperature and time. Without any low-surface-energy modification of the ZrPP films, the intrinsic hydrophobic characteristics of the surface functional groups allows the ZrPP films for a stable hydrophobicity with a CA ranging from 134° to 151°. The hydrophobic ZrPP film on copper substrate shows a low k value in the low-k range (k < 3.0) in the field of ULSI circuits. Meanwhile, the excellent hydrophobic nature of the film provides a good corrosion protection of the coated copper substrate with good mechanical stability. Our results suggest that the excellent hydrophobic ZrPP films prepared by in situ crystallization technique have potential application as dielectrics or metal anticorrosion coatings. Acknowledgment. This work was supported by the National Natural Science Foundation of China, 973 Program (No. 2009CB939802), the Program for New Century Excellent Talents in Universities (No. NCET-07-0055), and the Beijing Nova Program (No. 2007B021).
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