Enhancement on the Surface Hydrophobicity and ... - MDPI

materials Article

Enhancement on the Surface Hydrophobicity and Oleophobicity of an Organosilicon Film by Conformity Deposition and Surface Fluorination Etching Zheng-Wen Xu 1 , Yu-Kai Zhang 1 , Tai-Hong Chen 2 , Jin-How Chang 2 , Tsung-Hsin Lee 3 , Pei-Yu Li 1 and Day-Shan Liu 1, * 1 2 3

*

Institute of Electro-Optical and Material Science, National Formosa University, 63201 Yunlin, Taiwan; [email protected] (Z.-W.X.); [email protected] (Y.-K.Z.); [email protected] (P.-Y.L.) Additive Manufacturing and Laser Application, Industrial Technology Research Institute, 73445 Tainan, Taiwan; [email protected] (T.-H.C.); [email protected] (J.-H.C.) Metal Industries Research & Development Centre, 82151 Kaohsiung, Taiwan; [email protected] Correspondence: [email protected]; Tel.: +886-5-6315665

Received: 30 May 2018; Accepted: 25 June 2018; Published: 26 June 2018

Abstract: In this work, the surface morphology of a hydrophobic organosilicon film was modified as it was deposited onto a silver seed layer with nanoparticles. The surface hydrophobicity evaluated by the water contact angle was significantly increased from 100◦ to 128◦ originating from the surface of the organosilicon film becoming roughened, and was deeply relevant to the Ag seed layer conform deposition. In addition, the organosilicon film became surface oleophobic and the surface hydrophobicity was improved due to the formation of the inactive C-F chemical on the surface after the carbon tetrafluoride glow discharge etching. The surface hydrophobicity and oleophobicity of the organosilicon film could be further optimized with water and oleic contact angles of about 138◦ and 61◦ , respectively, after an adequate fluorination etching. Keywords: organosilicon film; silver seed layer; conformity deposition; hydrophobicity; oleophobicity; fluorination etching

1. Introduction Anti-fingerprint which keeps surface free of contamination from fingerprints and dirt, as well as making it easier to clean, has been applied on daily-used supplies. More recently, it becomes a critical added-value for application on high-end products such as all smartphones and tablet touch screens to improve aesthetic appearance and reduce maintenance cost. To realize the anti-fingerprint property, products with both surface hydrophobicity and oleophobicity are essential [1–3]. Unfortunately, surface repellence to both water and oleic droplets is not available for substrates or devices, since most activate to either water or oleic droplets [4–6]. Consequently, surface modification via coating an anti-fingerprint film is demanded to simultaneously achieve surface hydrophobicity and oleophobicity. To realize a surface inactive to water droplet, a lipid film composed of a nonpolar molecule which possesses low surface free energy is commonly deposited, resulting in a surface exhibiting hydrophobicity [7–9]. Commonly, the higher is the contact angle to the water droplet, the lower is the surface free energy [10,11]. In our previous work, we demonstrated that an organosilicon film abundant in nonpolar carbon-hydrogen (C-H) related chemical bonds that possess a low surface free energy of about 10 mN/m2 exhibited surface hydrophobicity with a water contact angle of about 100◦ [12,13]. Although the film exhibited hydrophobic surface, the degree of the water angle (WCA) is still far

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from that of a super-hydrophobic surface (WCA > 150◦ ) required for an anti-fingerprint coating application [1]. To approach the film with surface super-hydrophobicity, one method according to the reports announced by Wenzel and Cassie is to roughen the surface to reach a certain degree [14,15]. Recently, regular or random rough surface achieved by the lithographic-patterning, chemical-etching, and layer-by-layer assembly techniques to create a high aspect ratio topographic surface of a silicone- or siloxane-based film has been developed to result in the surface super-hydrophobicity with self-cleaning function [2,16–18]. However, although an apparent improvement on the surface hydrophobicity is achievable via roughening the film’s surface, the chemical bond configurations on the film surface mainly composed of the C-H bond showed oleophilicity [6,19]. Consequently, oil and oily substances such as fingerprints and grease are likely to adhere to such an oleophilic surface. Except for engineering the surface roughness, another method to improve the surface hydrophobicity is to introduce carbon-fluorine (C-F) related bonds in the silicone or siloxane matrix by either wet or dry chemical process to minimize the surface energy as well as reduce the chemical interaction to the water droplet. Moreover, because the fluorine atoms in the C-F bond are more electronegative to repel the oleic droplets, it is also reported that the resulting surface is oleophobic with an oleic contact angle (OCA) greater than 60◦ [17,20–23]. For instance, Hsieh et al. used one-step sol-gel method to prepare silica-based coatings with fluorine modification. They found that the incorporation of the fluorine atoms to a critical atomic ratio was responsible for a surface with the improved water and oil repellence [17]. Moreover, they also sprayed the copolymer solution of TiO2 nanoparticles and perfluoroalkyl onto the silicon substrate to achieve a surface with super-hydrophobicity and oleophobicity [20]. Cansoy et al. studied the effect on the advancing and receding water contact angles of the pattern size and geometry on the silicon wafer realized by deep reactive ion etching where the surface was hydrophobized through vapor phase reaction using the dimethyldichlorosilane solution. They found that both values were correlated with the pattern distance and diameter [18]. Basu et al. sprayed a polydimethylsiloxane (PDMS)-silica nanocomposite coating onto the glass substrate to realize the surface with super-hydrophobicity. They demonstrated that the surface of the PDMS-silica coating became oleophobicity when sprayed with a top-coating using the FAS-13 solution with a low surface energy [21]. However, although the above-mentioned sol-gel and spray methods for preparing silica-based film with the fluorine atoms incorporation are reported to realize the surface with quality hydrophobicity and oleophobicity, these two methods are challenged by the coating uniformity, thickness, and scale-up deposition. Recently, Aminayi et al. successfully applied a FOTS layer with the cotton fabric using nanoparticles deposition in the vapor phase reaction to perform surface ultra-oleophobicity. The nanoparticle roughened fabric surface caused a high static contact angle and a balance dynamic contact angle to the glycerol droplet [22]. In addition, Durret et al. prepared a roughened FEP (fluorinated Ethylene Propylene) flexible film by nano-imprint lithography. They discussed the evolutions of the surface wettability and contact angle hysteresis on the dimension of these nanostructures [23]. In addition to nanostructures prepared using imprint and vapor phase reaction technologies to possibly meet the requirement for depositing functional coatings on large-area substrates, the development of the self-organization of metals such as Au, Ag, and Ni films after a specific annealing treatment is also a promising candidate for achieving three-dimensional nanostructures on the scale-up substrate using vapor phase deposition [24–27]. In this work, we developed a combination process of the conformity deposition and surface fluorination etching to realize a quality hydrophobic organosilicon film with surface oleophobicity. Surface textures of the organosilicon film were modified and controllable, as it was deposited onto the silver seed layer with specific nanoparticles. The relationship between the surface of the organosilicon film and the Ag seed layer with nanoparticles was investigated by their surface and cross-section observations. Subsequently, carbon tetrafluoride (CF4 ) plasma was employed to etch the roughened organosilicon film. Evidence of the surface fluorination on the organosilicon film etched by the plasma treatment was conducted by the chemical bonds analysis. The C-F related bonds were abundant in the

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surface of the etched organosilicon film. The plasma treatment was elucidated to be responsible for the optimization of the surface hydrophobicity and the achievement of the surface oleophobicity. 2. Material Preparation and Experimental Procedure A silver seed layer prepared using the sputtering system was deposited onto the clean silicon substrate. The thickness of this seed layer was controlled at various deposition times from 75 to 720 s with a deposition rate about of 4 nm/min. To form the Ag nanoparticles, these silver seed layers were then annealed by a rapid thermal annealing (RTA) treatment at 500 ◦ C for 1 min under nitrogen ambient. After 100 nm-thick organosilicon films were plasma polymerized by the plasma enhanced chemical vapor deposition (PECVD) system at room temperature using the precursor of tetramethylsilane (Si(CH3 )4 , TMS) monomer, they were deposited onto the annealed silver seed layers. The deposition pressure, rf power, and gas flow rate of the TMS monomer were fixed at 26 Pa, 70 W, and 75 sccm, respectively. Eventually, the chemical bond configurations on the surface of the organosilicon film were modified by the fluorination etching under the CF4 glow discharge for various times (15–60 s). The etching pressure, rf power, temperature, and gas flow rate of the CF4 gas were controlled at 78 Pa, 250 W, 70 ◦ C, and 70 sccm, respectively. Another set of the organosilicon films directly deposited onto the silicon substrate with and without the fluorination etching also were prepared as the comparisons. Film thickness of these hydrophobic organosilicon films was measured using a surface profile system (Dektak 6M, Veeco, New York, NY, USA). Optical transmittance and absorbance of the silver seed layer were conducted by an UV-Vis-NIR spectrophotometer (UVD 3500, Labomed, Inc., Los Angeles, CA, USA). Surface roughness of the silver seed layers and the organosilicon films with and without the fluorination etching process was measured by atomic force microscopy (AFM, DI-3100, Veeco, New York, NY, USA) using the tapping mode. Plane-view and cross-section morphologies of the Ag nanoparticles as well as the organosilicon films deposited onto the Ag seed layers were observed by a field emission scanning electron microscope (FE-SEM, JSM-6700F, JEOL, Tokyo, Japan) operated at 3 kV. The chemical bond nature and functional groups of the films were examined by Fourier transform infrared (FTIR) spectrometry (FT/IR-4100, JASCO, Halifax, NS, Canada). The evolutions of the chemical bond configurations on the film surface with and without the fluorination etching were analyzed by an X-ray photoelectron spectroscope (XPS, ULVAC-PHI, Quantera SXM, Kanagawa, Japan) with monochromatic Al Kα radiation. Contact angles of the deionized water and hexadecane (C16 H34 ) liquid droplets on the film surface measured from a contact angle meter (FTA125, Contact Angle Analyzer, First Ten Angstroms, VA, USA) at least 10 times for each sample were employed to evaluate the surface wettability of the film structures to repel water and oil. 3. Results and Discussion Surface roughness of the as-deposited Ag seed layer deposited for 150 s and the Ag seed layer deposited for 75, 150, 480, and 720 s and then annealed at 500 ◦ C for 1 min under nitrogen ambient are given in Figure 1a–e, respectively. In Figure 1a, uniform needle-like structures are distributed over the surface of the as-deposited Ag seed layer with a low root-mean-square surface roughness, Rq , of about 2.0 nm. In contrast to the smooth surface, uneven tip-like structures were observed from the annealed Ag seed layer and the dimension of these structures was found to be increased as the deposition times increased (Figure 1b–e). Table 1 summarizes the surface roughness of these annealed Ag layers. Compared to the as-deposited Ag seed layer, the formation of the tip-like structures distributed over the surface of the annealed Ag seed layer corresponded to a marked increase in the surface roughness (~31.6 nm). In addition, the increase in the dimension of the tip-like structures on the annealed surface also resulted in the increase in the surface roughness. The larger were the tip-like structures observed on the film surface, the higher was the surface roughness measured. A highest surface roughness of about 76.0 nm was thus measured from the annealed Ag seed layer deposited for 720 s (Figure 1e). Figure 2b–e shows the surface morphologies of the annealed Ag seed layer as a function of the deposition time as well as the as-deposited Ag seed layer deposited for 150 s

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(Figure 2a). The particles distributed over the surface of the as-deposited Ag seed layer (Figure 2a) are densely and tightly packed, whereas round and separated nanoparticles were observed from the surface of the annealed samples. As quoted from the reports, the formation of these isolated Ag nanoparticles was ascribed to the compressive stress induced by the annealing treatment and the Ostwald ripening mechanism [28,29]. It was also evident that the size of these nanoparticles was increased with the deposition time of the Ag seed layer increasing. The mean diameters of these round nanoparticles calculated by the software ImageJ analysis are summarized in Table 1 [30]. The mean size of the nanoparticles for the annealed Ag seed layer deposited for 75 s was about 72 nm, while the thick Ag seed layer deposited for 720 s resulted in a large nanoparticle size of about 232 nm after the RTA treatment. The optical transmittance and absorbance spectra of the annealed Ag seed layer as a function of the deposition time are depicted in Figure 3a,b. As can be seen in Figure 3a, the opaque Ag seed layers with the transmittance of nearly 0% (not shown in the figure) became transparent after being processed by the RTA treatment as a consequence of the incident light leaked through the nanoparticle boundaries. The average transmittance at visible wavelengths (400~700 nm), Tave , as summarized in Table 1, decreased as the deposition time of the Ag seed layer increased. Average transmittances higher than 80% were obtained from the annealed Ag seed layers deposited for 75 and 150 s, while the thick Ag seed layers deposited for 480 s annealed by the RTA treatment corresponded to an average transmittance lower than 40%. Compared to the annealed Ag seed layer deposited for 480 s, the slight increase in the average transmittance of the annealed Ag seed layer deposited for 720 s (~46%) was ascribed to the reduction in the surface coverage of the Ag nanoparticles, as listed in Table 1. In addition, according to the literature [31–33], the obvious peak that appeared in the absorbance spectra of these annealed samples, as shown in Figure 3b, was in connection with the localized surface plasmon (LSP) resonance emerged from the formation of the Ag nanoparticles. Consistent with previous reports [34,35], the increase in the mean size of the Ag nanoparticles analyzed by the software ImageJ, as shown in Table 1, also corresponded to the red-shift of the absorbance peak in Figure 3b. According to the above experiments, size-dependent nanoparticles caused the evolution of the surface roughness, which were realized by controlling the deposition time of the Ag seed layer followed by an RTA treatment. Figure 4c,d shows the surface roughness of the hydrophobic organosilicon films deposited onto the annealed Ag seed layer deposited for 150 and 480 s, respectively. The organosilicon films directly deposited onto the silicon substrate and onto the as-deposited Ag seed layer surface, respectively, are also given in Figure 4a,b for comparison. The organosilicon film directly deposited onto the silicon substrate was quite smooth with a very low surface roughness of 0.4 nm. As the organosilicon film deposited onto the as-deposited Ag seed layer (Figure 4b), needle-like structures similar to those that appeared on the as-deposited Ag surface, as shown in Figure 1a, were observed to lead to a slight increase in the surface roughness (~1.9 nm). It was also noted that these needle-like structures distributed over the organosilicon film surface evolved into tip-like shape as it was deposited onto the annealed Ag seed layer, and also corresponded to a high surface roughness of about 18.1 nm, as shown in Figure 4c. Similar to the size-dependent of the Ag nanoparticles, the size of the tip-like structures on the organosilicon film surface also increased as the deposition time of the annealed Ag seed layer increased. A significant increase in the surface roughness (~49.8 nm) was measured from the organosilicon film deposited onto the annealed Ag seed layer deposited for 480 s (Figure 4d). Surface morphologies of the organosilicon films deposited onto the silicon substrate and the annealed Ag seed layer surface are shown in Figure 5a,b. The surface morphology of the organosilicon film seemed to be smooth and densely packed with obvious channels, as it was directly deposited onto the silicon substrate. By contrast, separated particles with various dimensions were observed on the surface morphology of the organosilicon film deposited onto the annealed Ag seed layer. Cross-section morphologies of the annealed Ag seed layer and the organosilicon film deposited onto this annealed seed layer are shown in Figure 5c,d. Semi-spherical structures appear in Figure 5d that are similar to the nanostructures observed in Figure 5c, further confirming that the organosilicon film grew confirmty

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nanostructures observed in Figure 5c, further confirming that the organosilicon film grew confirmty onthe theAgAg nanoparticles. Accordingly, significant in the surface ofroughness of the on nanoparticles. Accordingly, significant increaseincrease in the surface roughness the organosilicon organosilicon film that was comparable to that of with the Ag layer with the nanoparticles was film that was comparable to that of the Ag seed layer the seed nanoparticles was achievable from this achievable from this conform deposition, as presented in Figure 5e. conform deposition, as presented in Figure 5e.

Figure 1. Surface roughness of: (a) the as-deposited Ag seed layer; and (b–e) the Ag seed layer Figure 1. Surface roughness of: (a) the as-deposited Ag seed layer; and (b–e) the Ag seed layer deposited for 75, 150, 480, and 720 s, respectively, and then annealed at 500 ◦°C for 1 min under deposited for 75, 150, 480, and 720 s, respectively, and then annealed at 500 C for 1 min under nitrogen ambient. nitrogen ambient. Table 1. Surface roughness (Rq), mean particle size, average transmittance (Tave), surface coverage, Table 1. Surface roughness (Rq ), mean particle size, average transmittance (Tave ), surface coverage, and absorbance peak of the Ag seed layer deposited for various time after annealed at 500 °C for 1 min and absorbance peak of the Ag seed layer deposited for various time after annealed at 500 ◦ C for 1 min under nitrogen ambient. under nitrogen ambient.

Sample

Parameter

Parameter

Sample

Rq (nm) Rq (nm) Mean particle Mean particle sizesize (nm)(nm) Tavg (%) Tavg (%) Surface coverage (%) (%) Surface coverage Absorbance peak (nm) Absorbance peak (nm)

75 75 18.2 18.2 72 ± 44 72 ± 44 8686 20.4 20.4 411 411

Ag Deposition Time (s) Ag Deposition Time (s) 150 480 150 480 31.6 52.8 31.6 52.8 84 ± 66 181 84 ± 66 181±±9797 82 82 3535 22.9 41.3 22.9 41.3 417 437 417 437

720 720 76.0 76.0 232 232±±138 138 4646 28.1 28.1 438 438

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Figure 2. Topographicalimages images byFE-SEM FE-SEM observationsof: of: (a)the the as-depositedAg Ag seedlayer; layer; and Figure Figure2.2.Topographical Topographical imagesby by FE-SEMobservations observations of:(a) (a) theas-deposited as-deposited Agseed seed layer;and and (b–e) the theAg Ag seed seedlayer layer deposited depositedfor for 75, 75,150, 150, 480, 480,and and 720 720s,s, s,respectively, respectively, and then thenannealed annealed at 500 500°C ◦°C (b–e) (b–e)the Agseed layerdeposited for75, 150,480, and720 respectively,and andthen annealedatat500 C for 1 min under nitrogen ambient. for11min minunder undernitrogen nitrogenambient. ambient. for

(a) (a)

Transmittance Transmittance(%) (%)

100 100

80 80

60 60

Depositiontime time Deposition 75 s 75 s 150s s 150 480s s 480 720s s 720

40 40

20 20 400 400

500 500

600 600

Wavelength avelength(nm) (nm) W Figure 3. Cont.

700 700

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Absorbance(arb. unit) Absorbance(arb. unit)

(b)

Deposition time 75 s Deposition 150 s time 48075s s 720150 s s 480 s 720 s

(b)

400 400

500

600

W avelength (nm) 500

600

700 700

Figure 3. (a) Optical transmittance; and (b) absorbance spectra of the annealed Ag seed layers as a (nm) Figure 3. (a) Optical transmittance; and W (b) avelength absorbance spectra of the annealed Ag seed layers as a function functionofofthe thedeposition depositiontime. time. Figure 3. (a) Optical transmittance; and (b) absorbance spectra of the annealed Ag seed layers as a function of the deposition time.

Figure 4. Surface Roughness of: (a) the organosilicon film directly deposited onto the silicon substrate; and (b) the film deposited onto the as-deposited Ag seed layer; as well as the films Figure4.onto 4. Surface Roughness of:the (a)organosilicon the organosilicon film deposited onto the silicon deposited the Roughness annealed Ag layers deposited at for: (c) 150directly s; and (d) 480 s. Figure Surface of:seed (a) film directly deposited onto the silicon substrate; substrate; and (b) the film deposited onto the as-deposited Ag seed layer; as well as the and (b) the film deposited onto the as-deposited Ag seed layer; as well as the films deposited ontofilms the deposited annealed Ag seed layers deposited at for: annealed Agonto seedthe layers deposited at for: (c) 150 s; and (d) 480 (c) s. 150 s; and (d) 480 s.


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Figure Topographicalimages imagesby byFE-SEM FE-SEM observations observations of onto: (a)(a) Figure 5. 5. Topographical of the the organosilicon organosiliconfilms filmsdeposited deposited onto: the silicon substrate; and (b) the annealed Ag seed layer. Cross-section images by FE-SEM the silicon substrate; and (b) the annealed Ag seed layer. Cross-section images by FE-SEM observations observations of: (c) the annealed Ag seed layer; and (d) the organosilicon film deposited onto the of: (c) the annealed Ag seed layer; and (d) the organosilicon film deposited onto the annealed Ag seed annealed Ag seed layer. (e) A schematic representation of the conformity deposition. layer. (e) A schematic representation of the conformity deposition.

Surface hydrophobicity determined by the water droplets contacted to the organosilicon films Surface hydrophobicity by the droplets contacted the organosilicon films deposited onto the silicon determined substrate and ontowater the Ag seed layers withtoand without an RTA deposited onto the silicon substrate and onto the Ag seed layers with and without an RTA treatment treatment are shown in Figure 6a–d, respectively. The measured water contact angles and the arecorresponding shown in Figure 6a–d,roughness respectively. The measured angles and the corresponding surface are summarized in water Table contact 2. The surface hydrophilicity of the surface are summarized in angle Tableless 2. The hydrophilicity the asilicon siliconroughness substrate with a water contact than surface 40° became hydrophobicofwith water substrate contact angle of about 100°angle as it less wasthan modified by coating the organosilicon film contact (Figure angle 6a). A of slight with a water contact 40◦ became hydrophobic with a water about ◦ increase in the water contact angle of about 102° was measured from the surface of the 100 as it was modified by coating the organosilicon film (Figure 6a). A slight increase in the water ◦ organosilicon deposited the as-deposited Ag seedoflayer (Figure 6b), which concurrently contact angle of film about 102 wasonto measured from the surface the organosilicon film deposited onto only Ag a small increase in the surface as compared to thea small organosilicon theexhibited as-deposited seed layer (Figure 6b), whichroughness concurrently exhibited only increasefilm in the directly deposited the silicon substrate. The roughened surface of the organosilicon filmsubstrate. when surface roughness asonto compared to the organosilicon film directly deposited onto the silicon it was deposited onto the annealed Ag seed layer with nanoparticles, as observed in Figure The roughened surface of the organosilicon film when it was deposited onto the annealed Ag 4c, seed resulted in a large water contact angle of about 122° (Figure 6c), revealing that the significant layer with nanoparticles, as observed in Figure 4c, resulted in a large water contact angle of about 122◦ improvement on the hydrophobic property was achievable from the film deposited onto the (Figure 6c), revealing that the significant improvement on the hydrophobic property was achievable patterned Ag underlayer. The surface hydrophobicity could be further optimized to a water contact from the film deposited onto the patterned Ag underlayer. The surface hydrophobicity could be further angle of 128° as the organosilicon film deposited onto the annealed Ag seed layer deposited for 480 optimized to a water contact angle of 128◦ as the organosilicon film deposited onto the annealed Ag s (Figure 6d). As can be seen in Table 2, the evolution on the water contact angle of the seed layer deposited for 480 s (Figure 6d). As can be seen in Table 2, the evolution on the water contact organosilicon film was seen to be deeply relevant to the increase in the film’s surface roughness. A angle of the organosilicon film was seen to beasdeeply relevant to the increase in the surface simple model proposed by Wenzel equation, represented in following equation, canfilm’s be referred roughness. A simple model proposed by Wenzel equation, as represented in following equation, can be

where γ is the roughness factor defined as the ratio between the actual surface area of a rough surface to the projected area. Θ and Θ* are the contact angles of the liquid droplets on the flat and patterned surface, respectively. According to the relationship between the surface roughness and the hydrophobicity of the organosilicon film, one can achieve a quality hydrophobic surface simply Materials 2018, 11, 1089 9 of 18 by using the conformity deposition process which was demonstrated as the PECVD-deposited organosilicon film grew conformably to the patterned Ag seed layer with size-controlled nanoparticles prepared by an wettability RTA treatment through the film above-mentioned and referred to characterize the surface of the organosilicon surface affectedsurface by its surface cross-section observations. roughness [36]:

cosΘ∗ = γcosΘ

(1)

Table 2. Surface roughness, water contact angle, and oleic contact angle of the organosilicon film directly ontofactor the silicon substrate and ratio deposited onto the and annealed where γ is thedeposited roughness defined as the between theas-deposited actual surface area ofAg a rough * seed layer. surface to the projected area. Θ and Θ are the contact angles of the liquid droplets on the flat

and patterned surface, respectively. roughness Sample According to the relationship Rq (nm)between WCAthe (°) surface OCA (°) and the hydrophobicity of the organosilicon film, one can achieve a quality hydrophobic Organosilicon on silicon substrate 0.4 100 ± 0.2 11 ± 1.1surface simply by using the conformity deposition process which was demonstrated as the PECVD-deposited Organosilicon on as-deposited Ag seed layer 1.9 103 ± 0.6 10 ± 0.4 organosilicon film grewon conformably toseed the patterned Organosilicon annealed Ag layer (150 Ag s) seed layer 18.1 with size-controlled 122 ± 0.5 7nanoparticles ± 0.5 preparedOrganosilicon by an RTA treatment through the above-mentioned surface cross-section observations. on annealed Ag seed layer (480 s) 49.8 and 128 ± 0.8 3 ± 0.3

Figure 6. Water contact angle of: (a) the organosilicon film directly deposited onto the silicon Figure 6. Water contact angle of: (a) the organosilicon film directly deposited onto the silicon substrate; substrate; and (b) the film deposited onto the as-deposited Ag seed layer; as well as the films and (b) the film deposited onto the as-deposited Ag seed layer; as well as the films deposited onto deposited onto the annealed Ag seed layers deposited at for: (c) 150 s; and (d) 480 s (the inset figures the annealed Ag seed layers deposited at for: (c) 150 s; and (d) 480 s (the inset figures show the show the correspondent oleic contact angle). correspondent oleic contact angle).

However, though the specific area of the organosilicon film had been successfully enlarged as Table 2. Surface roughness, water contact angle, and oleic contact angle of the organosilicon film it was deposited onto the Ag nanoparticles and showed less activated to the water droplet to result directly deposited onto the silicon substrate and deposited onto the as-deposited and annealed Ag in a large water contact angle, this surface still was very sensitive to the oleic droplet. As can be seed layer. seen in the inset figures of Figure 6a,d, both samples showed oleophilic surface with the oleic contact angles of about 11° and 3°, respectively. To active the surface of the organosilicon film to Sample R (nm) WCA (◦ ) OCA (◦ ) q

Organosilicon on silicon substrate Organosilicon on as-deposited Ag seed layer Organosilicon on annealed Ag seed layer (150 s) Organosilicon on annealed Ag seed layer (480 s)

0.4 1.9 18.1 49.8

100 ± 0.2 103 ± 0.6 122 ± 0.5 128 ± 0.8

11 ± 1.1 10 ± 0.4 7 ± 0.5 3 ± 0.3

However, though the specific area of the organosilicon film had been successfully enlarged as it was deposited onto the Ag nanoparticles and showed less activated to the water droplet to result in a large water contact angle, this surface still was very sensitive to the oleic droplet. As can be seen in the inset figures of Figure 6a,d, both samples showed oleophilic surface with the oleic contact angles of about 11◦ and 3◦ , respectively. To active the surface of the organosilicon film to repel the oleic droplet, surface modification via engineering the chemical bond configuration was carried out by etching the

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film in the CF4 glow discharge. Figure 7 illustrates the etching thickness of the organosilicon film in the CF4 plasma ambient as a function of the etching times. The etching thickness of the organosilicon film was linearly correlated to the time of the film exposed to the CF4 plasma ambient. As the etching time reached 60 s, an average etching thickness of about 118 nm, exceeding 100 nm, was obtained. The surface roughness of the organosilicon films deposited onto the silicon substrate and onto the annealed Ag seed layer after etching by the CF4 plasma for 40 s is shown in Figure 8a,b, respectively. The surface roughness of the organosilicon films directly deposited onto the silicon substrate and onto the annealed Ag seed layer after treating by the CF4 plasma etching was only slightly increase to about 0.6 and 51.7 nm, respectively, as compared to the samples without the CF4 plasma treatment (Figure 4a,d). The correspondent surface morphologies of the etched organosilicon film investigated from the SEM observations, as shown in Figure 8c,d, are also very similar to those of the un-etched samples (Figure 5a,b). This revealed that the physical ion-bombardment to cause the change in the surface textures was less important than the chemical reaction to result in the bond-reconstruction on the organosilicon film induced by the CF4 plasma etching. Water contact angles of these two organosilicon films etched by the CF4 plasma for 40 s are presented in Figure 9a,b, respectively. The surface hydrophobicity of the organosilicon film directly deposition onto the silicon substrate evaluated from the water contact angle showed slight increase from 100◦ to 102◦ as it was treated by the CF4 plasma etching for 40 s, whereas the water contact angle of the organosilicon film deposited onto the annealed Ag seed layer was increased more significantly after the CF4 plasma etching. In addition, the surface of these etched organosilicon films became oleophobic with oleic contact angles of about 51◦ and 68◦ , as shown in Figure 9c,d, respectively. Table 3 summarizes the evolutions on the water and oleic contact angles of the organosilicon film directly deposited onto the silicon substrate and onto the annealed Ag seed layer after etching by the CF4 plasma for various times. Although the increase in the surface roughness of the flat organosilicon film directly deposited onto the silicon substrate etched by the CF4 plasma was very limited, its water contact (~103◦ ) was comparable to that of the organosilicon film deposited onto the as-deposited Ag seed layer which performed a higher surface roughness of about 1.9 nm, indicating the surface modification on the chemical bonds achieved by the CF4 plasma etching was also facilitated to optimize the film’s surface hydrophobicity. Moreover, the increase in the water contact angle of the etched organosilicon film was more evident as it was deposited onto the annealed Ag seed layer. Such textured surface of the organosilicon surface deposited onto the annealed Ag seed layer which might allow larger specific area to be chemically modified than that of the flat organosilicon film deposited onto the silicon substrate was likely to be responsible for the apparent increase in the water contact. The water contact angle listed in Table 3 was increased with the film surface etched by the CF4 plasma increasing, and a largest water contact angle of about 138◦ was measured from the organosilicon film surface etched by the CF4 plasma for 40 s. However, because the etching thickness exceeded the thickness of the organosilicon film (~100 nm), a drastic decrease in the water contact angle correlating to the surface wettability of the annealed Ag seed layer was thus measured (~70◦ ). In regard to the surface activity to the oleic droplets shown in Table 3, the surface of the organosilicon film became oleophobic with an oleic contact angle higher than 50◦ as it was chemically modified by the CF4 plasma. In addition, similar to the evolutions of the water contact angles of the organosilicon films etched by the CF4 plasma, the evolutions of the oleic contact angle were also strongly correlated to the films’ surface roughness. It was also noted that the surface of the etched organosilicon film again evolved into surface oleophilicity with an oleic contact angle of about 7◦ , a degree close to the oleic droplet on the annealed Ag seed layer (~3.1◦ ), as it was etched for 60 s in the CF4 plasma.

Sample Organosilicon on silicon Organosilicon on silicon substrate substrate Organosilicon on annealed Materials 2018, 11, 1089 Organosilicon on annealed Ag seed layer Ag seed layer

Etchingthickness thickness(nm) (nm) Etching

120 120

WCA (oo) WCA ( ) OCA (oo) OCA ( ) WCA (oo) WCA ( ) OCA (oo) OCA ( )

0 0 100 ± 0.2 100 ± 0.2 11 ± 1.1 11 ± 1.1 128 ± 0.8 128 ± 0.8 3 ± 0.3 3 ± 0.3

CF4 Plasma Etching Time (s) 15 30 40 15 30 40 104 ± 0.3 103 ± 0.2 103 ± 0.3 104 ± 0.3 103 ± 0.2 103 ± 0.3 50 ± 1.4 51 ± 1.0 51 ± 1.6 50 ± 1.4 51 ± 1.0 51 ± 1.6 132 ± 0.9 135 ± 0.8 138 ± 0.6 132 ± 0.9 135 ± 0.8 138 ± 0.6 60 ± 0.6 62 ± 0.9 66 ± 0.7 60 ± 0.6 62 ± 0.9 66 ± 0.7

60 60 103 ± 0.4 103 ± 0.4 50 ± 0.8 50 ± 0.8 70 ± 0.7 70 ± 0.7 11 of 18 7 ± 0.2 7 ± 0.2

Organosilicon film etched in CF 4 plasma Organosilicon film etched in CF 4 plasma

100 100 80 80 60 60 40 40 20 20 20 20

30

40

30 40 Etching time (sec) Etching time (sec)

50 50

60 60

Figure 7. Etching thickness of the organosilicon film treated by the CF4 plasma as a function of the Figure Figure 7. 7. Etching thickness of the organosilicon organosilicon film treated treated by by the the CF CF44 plasma as a function function of the the etching time. etching time. etching time.

Figure 8. Surface roughness and morphologies of the CF4 plasma etching for 40 s on the organosilicon etching 40 ss on on the the organosilicon organosilicon Figure 8. 8. Surface Surface roughness roughness and morphologies morphologies of of the the CF CF4 plasma Figure plasma etching for for film deposited onto: (a,c) theand silicon substrate; and (b,d) 4the as-deposited Ag 40 seed layer. film deposited onto: (a,c) the silicon substrate; and (b,d) the as-deposited Ag seed layer. film deposited onto: (a,c) the silicon substrate; and (b,d) the as-deposited Ag seed layer.


12 of 18 12 of 18

Figure 9. Water contact angles of: (a) the organosilicon film directly deposited onto the silicon

Figure 9. Water contact angles of: (a) the organosilicon film directly deposited onto the silicon substrate; substrate; and (b) the film deposited onto the annealed Ag seed layer after etching by the CF4 and (b) the film deposited onto the annealed Ag seed layer after etching by the CF4 plasma for 40 s; plasma for 40 s; and (c,d) the corresponding oleic contact angles (the inset images show the water and (c,d) the corresponding oleic contact angles (the inset images show the water and oleic droplets on and oleic droplets on the film surface). the film surface).

FTIR spectra of the organosilicon film before and after the CF4 plasma etching for 40 s are contact contactofangle of the organosilicon film directly deposited Table 3. Water illustrates in Figure 10.angle The and FTIRoleic spectrum the organosilicon film etched by the CF 4 plasma onto was the silicon substrate and deposited onto the annealed Ag seed layer after etching by the CF4 plasma for almost identical to that of the film without the CF4 plasma etching. Four absorbance peaks various time. over these two FTIR spectra. The broad absorbance band with peaks at about 797 predominated and 835 cm−1, and a sharp peak at about 1253 cm−1 were denoted as the deformation of the Si-C CF4 Plasma Etching Time broad (s) rocking vibration and symmetric bending in the Si-CH3 groups, while another signal located Sample −1 at high wavenumbers of about 2899 and0 2955 cm was as the hydrophobic bond 15 characterized 30 40 60 associated with the C-HWCA bond symmetrical and asymmetrical of CH3 103 groups (o ) in the100 ± 0.2 104 ± 0.3 103 ± 0.2 stretching 103 ± 0.3 ± 0.4 Organosilicon on silicon ) about111047 ± 1.1 cm−1 was 50 ±assigned 1.4 51 1.0 networks 51 ± of 1.6 the Si-CH 50 ±2-Si 0.8 substrate [37–40]. The absorbance OCA peak(oat as ±the o Organosilicon on annealed bond overlapped with the Si-O( )stretching mode to WCA 128 ±vibration 0.8 132 ± 0.9in the Si-O-C 135 ± 0.8bond [13,41]. 138 ± 0.6In contrast 70 ± 0.7 seed layer film without OCA (othe ) CF4 plasma 3 ± 0.3 etching, 60 ± 0.6 62 0.9 66 cm ± 0.7 ± the 0.2 −1 related7to the Ag organosilicon a shoulder at ± around 1128 absorbance that emerged from the C-F chemical bond, as observed in the etched organosilicon film [42–44]. Figure shows the XPS survey spectra taken the surface of the organosilicon film FTIR spectra of11a,b the organosilicon film before and after theonCF 4 plasma etching for 40 s are illustrates with and without the CF 4 plasma etching. The surface of the organosilicon film without the CF4 in Figure 10. The FTIR spectrum of the organosilicon film etched by the CF4 plasma was almost identical to etching was dominated by the elements of C, Si, Si, and O. By contrast, the intensity of the C, Si, and that of the film without the CF4 plasma etching. Four absorbance peaks predominated over these two FTIR O signal was apparently decreased and the element of F became the dominant signal over the spectra. The broad absorbance band with peaks at about 797 and 835 cm−1 , and a sharp peak at about surface of the organosilicon film etched by the CF4 plasma, showing evidence of the introduced −1 were denoted as the deformation of the Si-C rocking vibration and symmetric bending in the 1253 cm fluorine atoms on the film surface. In addition, very weak Ag signal could be observed from the −1 was Si-CHetched while another signal located at high wavenumbers about 2899 and 2955for cmthe 3 groups, organosilicon film.broad The high-resolution XPS spectra of the Si 2pofand C 1s core levels characterized as thefilms hydrophobic bond associated with the C-Hetching bond inare thepresented symmetrical and asymmetrical organosilicon with and without the CF 4 plasma in Figure 12a,b, −1with stretching of CH3 groups [37–40]. The absorbance at about 1047 was and assigned as the respectively. In Figure 12a, the surface of the peak organosilicon film cm both without thenetworks CF4 a peak at around eV. This peak could beindeconvoluted into [13,41]. three In of theplasma Si-CH2etching -Si bondshowed overlapped with the Si-O101.2 stretching vibration mode the Si-O-C bond −1 related major peaks at 99.9, 101.0, 102.1 the eV, CF which were in turn characterized as the chemical bond contrast to the organosilicon filmand without 4 plasma etching, a shoulder at around 1128 cm states of Si-Si, Si-C, and Si-O-C [45–47]. The surface of the organosilicon film without the plasma to the absorbance that emerged from the C-F chemical bond, as observed in the etched organosilicon etching was basically constructed from the cross-linking Si-C bond. When the film etched by the film [42–44]. Figure 11a,b shows the XPS survey spectra taken on the surface of the organosilicon film with CF4 plasma, the ion-bombardment damage induced by the CF4 plasma caused the breaking of the and without the CF4 plasma etching. The surface of the organosilicon film without the CF4 etching was Si-C chemical bond seemed to be responsible for the obvious reduction in the relative intense. The dominated by the elements C, Si, Si, O. By contrast, the intensity of the C, and 12b O signal C 1s core levels on theofsurface of and the unetched organosilicon film shown in Si, Figure only was apparently decreased and the element became the eV. dominant signal over the surface of theC-related organosilicon presented an intense C 1s signal of atFabout 284.3 This peak was composed of three

film etched by the CF4 plasma, showing evidence of the introduced fluorine atoms on the film surface. In addition, very weak Ag signal could be observed from the etched organosilicon film. The high-resolution XPS spectra of the Si 2p and C 1s core levels for the organosilicon films with and without the CF4 plasma

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etching are presented in Figure 12a,b, respectively. In Figure 12a, the surface of the organosilicon film both with and without the CF4 plasma etching showed a peak at around 101.2 eV. This peak could be deconvoluted into three major peaks at 99.9, 101.0, and 102.1 eV, which were in turn characterized as the chemical bond states of Si-Si, Si-C, and Si-O-C [45–47]. The surface of the organosilicon film without the plasma etching was basically constructed from the cross-linking Si-C bond. When the film etched by the CF4 plasma, the ion-bombardment damage induced by the CF4 plasma caused the breaking of the Si-C chemical bond seemed to be responsible for the obvious reduction in the relative intense. The C 1s core levels on the surface of the unetched organosilicon film shown in Figure 12b only presented an intense C 1s signal at about 284.3 eV. This peak was composed of three C-related bonds at about 283.8, Materials 2018,eV, 11, xrespectively, FOR PEER REVIEW 13 of 18chemical 284.5, and 285.8 which could be assigned as the Si-C, C-C/C-H, and Si-O-C bonds [48,49]. At the surface of the organosilicon film etched by the CF4 plasma, an apparent tail extending bonds at about 283.8, 284.5, and 285.8 eV, respectively, which could be assigned as the Si-C, to the high binding other than the[48,49]. main At C 1s at of 284.3 eV was measured. According C-C/C-H, and energy Si-O-C chemical bonds thepeak surface the organosilicon film etched by the to the literature [50–52], this tail could be deconvoluted into four specific peaks associated with the C-O, CF4 plasma, an apparent tail extending to the high binding energy other than the main C 1s peak at CF-CF2 , 284.3 was measured. the literature [50–52], taileV, could be deconvoluted into -CF2 , and -CFeV bondsAccording at about to 286.5, 289.3, 291.4, andthis 293.2 respectively. The formation of 3 chemical four specific peaks associated withwas the strong C-O, CF-CF 2, -CF2, and -CF3 chemical bonds at about 286.5, these fluorine-related chemical bonds evidence of the achievement on the surface fluorination 289.3, 291.4, and 293.2 eV, respectively. The formation of these fluorine-related chemical bonds was using the CF4 plasma etching. In addition, since these fluorinated groups was helpful to lower the surface strong evidence of the achievement on the surface fluorination using the CF4 plasma etching. In energy addition, of the organosilicon especially for the to possess the lowest 3 bond since these film, fluorinated groups was-CF helpful towhich lower was the reported surface energy of the surface organosilicon energy among these groups [20,53]. Thus, this surface presented quality repellence to water and film, especially for the -CF3 bond which was reported to possess the lowest surface oleic droplets. Consequently, the surface of thethis organosilicon film abundant in the C-F energy among these groups [20,53]. Thus, surface presented quality repellence to functional water and groups oleic droplets.water Consequently, the surface the only organosilicon filmfrom abundant in the C-F functional exhibited a superior contact angle to theoffilm constructed the Si-C/Si-O-C groups and also groups exhibited a superior water contact angle to the film only constructed from the Si-C/Si-O-C evolved surface oleophobicity when it was treated by the CF4 plasma etching. Figure 13a,b, respectively, groups and also evolved surface oleophobicity when it was treated by the CF4 plasma etching. depicts the core levels of the F 1s and Ag 3d signal measured on the surface of the etched organosilicon Figure 13a,b, respectively, depicts the core levels of the F 1s and Ag 3d signal measured on the film. Assurface can beofseen in Figure 13a, the fluorinated ofFigure the organosilicon film using theofCF the etched organosilicon film. As can surface be seen in 13a, the fluorinated surface the4 plasma treatment shows anfilm obvious at4 about eV that was as C-F chemical [54,55]. In organosilicon usingpeak the CF plasma688.4 treatment shows anassigned obvious peak at about 688.4bond eV that was assigned chemical bond368.1 [54,55]. In 374.3 addition, peaks at13b approximately 368.1 and 374.3chemical addition, the peaks as atC-F approximately and eVthe in Figure were identified as the 0 3d Figure 13b identified as0the chemical state of the metallic Ag (denoted as Ag0 3d5/2 and state of eV theinmetallic Agwere (denoted as Ag 3d5/2 and Ag 3/2 , respectively), in accordance with previous 0 3d3/2, respectively), in accordance with previous reports [56,57]. The metallic Ag signal likely reports Ag [56,57]. The metallic Ag signal likely emerged from the annealed Ag seed layer. According to the emerged from the annealed Ag seed layer. According to the investigations on the FTIR and XPS investigations on the FTIR and XPS measurements, the fluorine atoms were successfully introduced into measurements, the fluorine atoms were successfully introduced into the surface of the the surface of the organosilicon using the CF4toplasma etching to C-F form the nonpolar C-F chemical organosilicon film using the film CF4 plasma etching form the nonpolar chemical bond, thereby bond, thereby optimizing film’senergy surfacetoenergy to the improve surface hydrophobicity further further optimizing the film’sthe surface improve surfacethe hydrophobicity as well as as well achieve an oleophobic surface. as achieve an oleophobic surface.

Absorbance (arb.unit)

Si-CH 2-Si/Si-O-C

3500

Si-(CH 3) X

C-F

C-H

Si-CH 3

Etched organosilicon film

Unetched organosilicon film 3000

2500

2000

1500 -1

W avenumber (cm )

1000

500

10. FTIR spectra of the organosilicon film film before after the the CF4 CF plasma etching for 40 s. Figure Figure 10. FTIR spectra of the organosilicon beforeand and after 4 plasma etching for 40 s.


14 of 18 14 of 18

(a)


F1s

14 of 18

FKLL

(a)FKLL1


F1s

Ag3s

Ag3p O1s

Ag3d C1s

FKLL FKLL1 FKLL2

Intensity (arb. unit)


Materials 2018, 11, x FOR PEER REVIEW

Si2s Si2p Ag3s

(b)

Ag3p O1s

Ag3d C1s

Unetched organosilicon film FKLL2

C1s

Si2s Si2p

O1s

(b)

Unetched organosilicon film

C1s

O1s

Si2s Si2p

OKLL

Si2s Si2p

OKLL

1000

800

600

400

200

0

Binding energy (eV)

1000

800

600

400

200

0

Binding energy (eV)

Figure XPS Figure 11. 11. XPS survey survey spectra spectrataken taken on on the the surface surface of of the the organosilicon organosilicon film film (a) (a) with with and and (b) (b) without without Figure 11. XPS survey spectra taken on the surface of the organosilicon film (a) with and (b) without the etching. the CF CF44plasma plasma etching. the CF4 plasma etching. EEt cthc ehde d o r go ar ng oasni lic o soinlicf ilom n f il m

(a ) (a ) Intensity (arb. unit)


S i 2 Sp i 2 p

S i- C S i- S i

S i- S i

U n e t c h e d o r g a n o s i lic o n f il m U nSei-t cCh e d o r g a n o s i lic o n f il m

Si 2p

Si 2p

S i- C

S i-O -C

S i-S i

S i-O -C 106

104

102

S i -9S8i

100

96

B in d in g e n e r g y (e V ) 106

104

(b )

102 100 E tch e d o r g a n o silic o n f ilm

B in d in g e n e r g y (e V )

C 1s


-C F 3

C 1s

8 /C -H C9 -C

S i-O -C e d oCrFg-C a nF o2 silic o n f ilm -CE F tch 2 C -O

(b )


S i- C

S i- O - C

S i- O - C

C-C1F s3

C -C /C -H S i-C

S i-O -C

C F -C F 2

-C F 2

C -O

C -C /C -HS i-C

U n e tc h ed o r g a n o silic o n f ilm

S i-C

S i-O -C

C 1s

C -C /C -H

U n e tc h ed o r g a n o silic o n f ilm 296

294

292

290

96

288

286


284

282

S i-C

S i-O -C

Figure 12. XPS spectra of the (a) Si 2p and (b) C 1s core levels for the organosilicon films with and

Figure 12. XPS spectra of the (a) Si 2p and (b) C 1s core levels for the organosilicon films with and without the CF4 plasma etching. without the CF4 plasma etching. 296

294

292

290

288

286


284

282

Figure 12. XPS spectra of the (a) Si 2p and (b) C 1s core levels for the organosilicon films with and without the CF4 plasma etching.


(a )

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F 1s


C -F

692

690

688

686

684


(b )

A g 3d 0

Intensity (arb. unit) 378

A g 3 d 5 /2

0

A g 3 d 3 /2

376

374

372

370

368

366

364

B in d in g e n e r g y ( e V ) Figure of the the (a) (a)FF2s 2sand and(b) (b)Ag Ag3d3dcore corelevels levels organosilicon films etched by Figure 13. 13. XPS XPS spectra of forfor thethe organosilicon films etched by the 4 plasma. the CF CF4 plasma.

4. 4. Conclusions Conclusions Surface textures of ofaahydrophobic hydrophobicorganosilicon organosilicon film were simply modified by Ag theseed Ag layer. seed Surface textures film were simply modified by the layer. Size-dependent nanoparticles Aglayer seedannealed layer annealed 500 1°C forunder 1 minnitrogen under Size-dependent nanoparticles of the of Agthe seed at 500 ◦at C for min nitrogen ambient were obtained from the seed layer deposited for different time. The subsequently ambient were obtained from the seed layer deposited for different time. The subsequently deposited deposited organosilicon filmPECVD using system the PECVD system to growtoconformably to theSuch Ag organosilicon film using the was found to was growfound conformably the Ag seed layer. seed layer. Such a of roughened surface film of the organosilicon filmlayer similar to thebyAg layer a roughened surface the organosilicon similar to the Ag seed controlled the seed conformity controlled by the conformity deposition realized the improvement on the resulting surface deposition realized the improvement on the resulting surface hydrophobicity. The water contact angle hydrophobicity. The water contact angle organosilicon film deposited onto the annealedatAg of the organosilicon film deposited onto of thethe annealed Ag seed layer with the nanoparticles an ◦ seed layer with the nanoparticles at an average size of 181 ± 97 nm was apparently increase to 128° average size of 181 ± 97 nm was apparently increase to 128 as compared to the organosilicon film ◦ ). Moreover, as compared to the organosilicon filmsubstrate directly (~100 deposited onto thethe flat silicon bond substrate directly deposited onto the flat silicon chemical states(~100°). on the Moreover, the chemical bond states on the surface of the organosilicon film were modified using surface of the organosilicon film were modified using CF4 plasma etching. Although little change on CF 4 plasma etching. Although little change on the surface roughness was measured from the the surface roughness was measured from the organosilicon film etched by the CF4 plasma, the surface organosilicon film the CF4 plasma, the was further optimized, hydrophobicity wasetched furtherby optimized, especially forsurface the filmhydrophobicity with surface textures that allowed more especially for the film with surface textures that allowed more specific area for the surface specific area for the surface fluorination. The reason for the enhanced surface hydrophobicity of fluorination. The reason for the enhanced hydrophobicity of C-F the etched film the etched organosilicon film was ascribedsurface to the appearance of the related organosilicon functional groups was ascribed to the formed appearance of CF the C-F related functional groups on the film surface formed on the film surface during 4 plasma etching. Such etched surface abundant in the C-F during CF 4 plasma etching. Such etched surface abundant in the C-F bonds also evolved from bonds also evolved from oleophilic into oleophobic because of the C-F bonds, thus was inactive to the oleophilic intoAccordingly, oleophobic an because of the film C-F with bonds, thusand was inactive the oleic droplet. oleic droplet. organosilicon water oleic contacttoangles of about 138◦ Accordingly, an organosilicon filmfrom withthe water oleic contact angles of the about 138° and 60°, and 60◦ , respectively, was achieved film and conformably deposited onto annealed Ag seed respectively, was achieved from the film conformably deposited onto the annealed Ag seed layer with the nanoparticles, and then etched by the CF4 plasma treatment for 40 s. This functional film,

Materials 2018, 11, 1089

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layer with the nanoparticles, and then etched by the CF4 plasma treatment for 40 s. This functional film, exhibiting both surface hydrophobicity and oleophobicity, is a promising candidate for a quality anti-fingerprint coating. Author Contributions: D.-S.L. organized and designed the experiment procedures; T.-H.C. and J.-H.C. wrote this paper; Z.-W.X. and Y.-K.Z. executed the film deposition; and P.-Y.L. and T.-H.L. performed and supported the thin film measurements and analysis. All authors read and approved the final version of the manuscript to be submitted. Funding: This research was funded by Ministry of Science and Technology [MOST 105-2622-E-150-004-CC2] Industrial Technology Research Institute [A200-106BA2], and Metal Industries Research & Development Centre. Conflicts of Interest: The authors declare that there is no conflict of interests regarding the publication of this paper.

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