Optical, Electrical, and Surface Properties of Cu/Plasma Polymer Fluorocarbon Nanocomposite Thin Film Fabricated Using Metal/Polymer Composite Target

Sung  Hyun Kim; Mac Kim; Jae  Seong Park; Sang-Jin Lee

doi:10.3390/app9071296

Optical, Electrical, and Surface Properties of Cu/Plasma Polymer Fluorocarbon Nanocomposite Thin Film Fabricated Using Metal/Polymer Composite Target

Kim, Sung Hyun;Kim, Mac;Park, Jae Seong;Lee, Sang-Jin 2019-03-28 00:00:00 applied sciences Article Optical, Electrical, and Surface Properties of Cu/Plasma Polymer Fluorocarbon Nanocomposite Thin Film Fabricated Using Metal/Polymer Composite Target Sung Hyun Kim, Mac Kim, Jae Seong Park and Sang-Jin Lee * Chemical Materials Solutions Center, Korea Research Institute of Chemical Technology, Daejeon 34114, Korea; wdy1332@krict.re.kr (S.H.K.); kimmac79@krict.re.kr (M.K.); jspark@krict.re.kr (J.S.P.) * Correspondence: leesj@krict.re.kr; Tel.: +82-42-860-7902, Fax.: +82-42-860-7909 Received: 27 February 2019; Accepted: 26 March 2019; Published: 28 March 2019 Abstract: We propose a new method of fabricating metal–polymer composite targets for sputtering, which makes it easier to control the composition and enables the homogeneous and reproducible fabrication of metal–polymer nanocomposites over large areas. Using Cu/polytetraﬂuoroethylene composite targets containing 20, 50, and 80 wt.% Cu, Cu/plasma polymer ﬂuorocarbon (PPFC) nanocomposite thin ﬁlms were prepared by radio-frequency (RF) sputtering. Targets with 80 wt.% Cu were conductive; moreover, sputtering was possible not only with RF but also with mid-range frequency (MF) and direct current (DC) power sources. The nanocomposite thin ﬁlm deposited by MF and DC power using an 80 wt.% Cu target showed near-metallic characteristics, exhibited absorption peaks at 618 and 678 nm, and had a surface resistance of 2 10 and 34.55 W/sq, respectively. We also analyzed the structure and composition of the Cu/PPFC nanocomposite ﬁlms by X-ray diffraction and X-ray photoelectron spectroscopy. The described metal–polymer targets can advance the applications and commercialization of nanocomposite thin ﬁlms. Keywords: Cu/polytetraﬂuoroethylene composite target; plasma polymer ﬂuorocarbon; nanocomposite thin ﬁlm; sputtering power source; surface plasmon resonance 1. Introduction Polymer–metal nanocomposites exhibit excellent optical [1–8], electrical [1,4], and mechanical properties [9,10] and have been attracting much attention owing to their various characteristics such as surface hardness [6], bioactivity [11,12], perfect absorbance, [13–15], and sensing ability [16]. Polymers with good insulating properties are well suited as host materials for supporting a variety of metal clusters [5,17]. The excellent properties of polymer–metal nanocomposites depend on the size, quantity, and shape of various metal clusters contained in the polymer matrix; various studies elucidating these properties have been performed [17,18], with reference to surface antimicrobials and abrasion-resistant coatings, and gas sensor ﬁlms [19–22]. As a polymer matrix, polytetraﬂuoroethylene (PTFE), which is mechanically, thermally, and chemically stable, and has excellent insulation and optical properties, is widely used [1,3,6,9,11,19,23]. Studies using noble metals such as Ag [5,9,11,19,24–26], Au [3,16,27], and Cu [12–14] have been carried out, but mostly, Ag and Au have been used. In addition to noble metals, nanocomposites using SiO [6], graphite [10], ZnO [19], Ti [28], Fe–Ni–Co [29], and TiO [30], with PTFE, have also been reported. A nanocomposite can be fabricated by the physical vapor deposition (PVD) method, as PVD allows for control of the dopant, enables uniform coating, and minimizes the reaction with air. The co-sputtering method employing two sputtering cathodes [3,6,9,10,12–14,19,28] is the Appl. Sci. 2019, 9, 1296; doi:10.3390/app9071296 www.mdpi.com/journal/applsci Appl. Sci. 2019, 9, 1296 2 of 10 most widely used method, and other methods involve the use of an evaporator [9,25], sputter evaporator, ion beam co-sputtering [16], and pulsed laser deposition [24], to fabricate a polymer–metal nanocomposite. However, the use of two sputtering cathodes or a combination of two deposition methods to fabricate nanocomposites requires precise control for yield matching; moreover, it is difﬁcult to ensure reproducibility of the experimental results owing to the complicated equipment conﬁguration and difﬁculty in securing uniformity over a large area, which are stumbling blocks toward commercialization. In a previous study, our group found that a plasma polymer ﬂuorocarbon (PPFC) thin ﬁlm prepared using a carbon nanotube (CNT)/PTFE composite sputtering target exhibited diverse physical properties depending on the content of the CNT. In addition, it has been reported that CNT, when added to a composite target, imparts conductivity; hence, sputtering is also possible using a mid-range frequency (MF) power source [31]. Taking our previous study forward, in this study, a Cu/PTFE composite target for sputtering was ﬁrst introduced for fabricating a Cu/PPFC nanocomposite thin ﬁlm by uniformly dispersing Cu metal powder in PTFE powder and pressing at high temperature. Previously, the composite target was prepared by attaching half of the polymer target to half of the metal target, or attaching a metal foil or wire to the surface of the polymer target [1,6]. However, in those studies, it was challenging to deposit a nanocomposite thin ﬁlm of uniform composition ratio over a large substrate area and prepare a reproducible target; therefore, practical composite targets have been difﬁcult to achieve thus far. We fabricated noble polymer–metal composite targets with 20, 50, and 80 wt.% Cu in PTFE powder. Thus, the ﬁlling ratio of the metal nanoclusters in the nanocomposite thin ﬁlm can be easily controlled, and the nanocomposite thin ﬁlm can be prepared by long-duration sputtering with one target in the same manner as the conventional sputtering target, enabling excellent reproducibility. Finally, because of the controllability and simple equipment conﬁguration, large-area sputtering is possible; hence, this method can be employed in a wide variety of polymer–metal nanocomposite technical and commercial applications. In this study, we investigated the physical and chemical properties of the Cu/PPFC nanocomposite thin ﬁlms with various Cu contents, and analyzed how the properties of the ﬁlms change with radio-frequency (RF), MF, and direct current (DC) power sources using the Cu/PTFE (20:80, w/w) target. 2. Materials and Methods 2.1. Preparation of Cu/PTFE Composite Sputtering Targets Cu powder (e-Cu25, Chang Sung) was mixed with PTFE powder (A7, DuPont) at weight ratios of 20:80, 50:50, and 80:20, respectively, following which composite sputtering Cu/PTFE targets were prepared by a high-temperature compression molding method. Compression pressure was 200 kgf/cm and molding temperature was 370 C. A pure PTFE sputtering target devoid of any Cu powder was also prepared by the same method for reference. Disk-type Cu/PTFE composite sputtering targets with a diameter of 10.16 cm and thickness of 0.64 cm were then fabricated by milling. For simplicity, the targets were labeled PTFE (Cu 0), Cu 20, Cu 50, and Cu 80 according to the composition ratio. Figure 1a sequentially shows the fabrication of the Cu/PTFE composite target. Appl. Sci. 2019, 9, 1296 3 of 10 Appl. Sci. 2019, 9, x FOR PEER REVIEW 3 of 10 Figure 1. (a) Sequential diagram of the fabrication of Cu/PTFE composite target. (b) Illustration of the Figure 1. (a) Sequential diagram of the fabrication of Cu/PTFE composite target. (b) Illustration of the sputtering process to deposit Cu/plasma polymer ﬂuorocarbon (PPFC) nanocomposite thin ﬁlms with sputtering process to deposit Cu/plasma polymer fluorocarbon (PPFC) nanocomposite thin films radio frequency (RF), mid-range frequency (MF), and direct current (DC) power sources. with radio frequency (RF), mid-range frequency (MF), and direct current (DC) power sources. 2.2. Fabrication of Cu/PPFC Nanocomposite Thin Films 2.2. Fabrication of Cu/PPFC Nanocomposite Thin Films The sputtering chamber was evacuated to a base pressure of 6.6 10 Pa by a mechanical pump −3 The sputtering chamber was evacuated to a base pressure of 6.6 × 10 Pa by a mechanical pump and a cryogenic pump. The partial pressure of Ar during the process was 0.93 Pa. The Cu/PPFC and a cryogenic pump. The partial pressure of Ar during the process was 0.93 Pa. The Cu/PPFC nanocomposite thin ﬁlms were fabricated using RF (13.56 MHz), MF (40 kHz), and DC power with a nanocomposite thin films were fabricated using RF (13.56 MHz), MF (40 kHz), and DC power with a sputtering power density of 1.23 W/cm . Dual magnetron cathodes were used for MF sputtering to sputtering power density of 1.23 W/cm . Dual magnetron cathodes were used for MF sputtering to improve sputtering efﬁciency. Target-to-substrate distance was ﬁxed at 24 cm. A schematic diagram improve sputtering efficiency. Target-to-substrate distance was fixed at 24 cm. A schematic diagram of the sputtering process for each power source is shown in Figure 1b. We used a polyethylene of the sputtering process for each power source is shown in Figure 1b. We used a polyethylene terephthalate (PET, KIMOTO, Japan) ﬁlm substrate of size 20 20 cm and thickness 125 m. In order terephthalate (PET, KIMOTO, Japan) film substrate of size 20 × 20 cm and thickness 125 μm. In to compare the physical properties of the thin ﬁlms with different Cu composition ratios, pure PTFE, order to compare the physical properties of the thin films with different Cu composition ratios, pure Cu 20, Cu 50, and Cu 80 composite targets were sputtered with an RF power source to fabricate the PTFE, Cu 20, Cu 50, and Cu 80 composite targets were sputtered with an RF power source to thin ﬁlms. Deposition rates for each composite target and sputtering power source were determined fabricate the thin films. Deposition rates for each composite target and sputtering power source were by using the Alpha step method (Dektak XT, Bruker, MA, USA). A thickness step is generated by determined by using the Alpha step method (Dektak XT, Bruker, MA, USA). A thickness step is covering a part of the sample for measurement. To investigate the physical properties of the Cu/PPFC generated by covering a part of the sample for measurement. To investigate the physical properties nanocomposite thin ﬁlms according to power source, 100 nm thin ﬁlms were fabricated by sputtering of the Cu/PPFC nanocomposite thin films according to power source, 100 nm thin films were with RF, MF, and DC power sources using the Cu 80 composite target. The fabricated thin ﬁlms were fabricated by sputtering with RF, MF, and DC power sources using the Cu 80 composite target. The named “target name + power source type” for clarity and conciseness. For example, a thin ﬁlm made fabricated thin films were named “target name + power source type” for clarity and conciseness. For by an RF power source using a Cu 20 composite target is named “Cu 20 RF”, whereas that made by a example, a thin film made by an RF power source using a Cu 20 composite target is named “Cu 20 DC power source using a Cu 80 composite target is named “Cu 80 DC”. RF”, whereas that made by a DC power source using a Cu 80 composite target is named “Cu 80 DC”. 2.3. Characterization of Cu/PPFC Nanocomposite Thin Films 2.3. Characterization of Cu/PPFC Nanocomposite Thin Films The nanocomposite structure of Cu/PPFC thin ﬁlm was investigated by ﬁeld-emission The nanocomposite structure of Cu/PPFC thin film was investigated by field-emission transmission electron microscopy (FE-TEM, Tecnai G2 F30 S-Twin, FEI Co., Hillsboro, OR, USA). transmission electron microscopy (FE-TEM, Tecnai G2 F30 S-Twin, FEI Co., Hillsboro, OR, USA). Optical properties of the thin ﬁlms were measured by UV–VIS spectroscopy (U-4100, Hitachi, Tokyo, Optical properties of the thin films were measured by UV–VIS spectroscopy (U-4100, Hitachi, Japan). Standard deviation of water contact angle, sheet resistance, optical transmittance, and b* Tokyo, Japan). Standard deviation of water contact angle, sheet resistance, optical transmittance, (yellow index) were measured by ﬁve points at each sample. The measuring points were the center and b* (yellow index) were measured by five points at each sample. The measuring points were the and four sides of the ﬁlm. The surface energy of the nanocomposite thin ﬁlm was measured using a center and four sides of the film. The surface energy of the nanocomposite thin film was measured contact angle analyzer (Phoenix 300 Touch, Surface Electro Optics, Suwon, Korea). The volume of water using a contact angle analyzer (Phoenix 300 Touch, Surface Electro Optics, Suwon, Korea). The droplets was 2 L, and the images were automatically analyzed by the system. Structural characteristics volume of water droplets was 2 μL, and the images were automatically analyzed by the system. Structural characteristics of the Cu/PPFC nanocomposite thin films were analyzed by X-ray Appl. Sci. 2019, 9, 1296 4 of 10 Appl. Sci. 2019, 9, x FOR PEER REVIEW 4 of 10 photoelectron spectroscopy (XPS, AXIS Nova, Kratos, Manchester, UK) and X-ray diffraction (XRD, of the Cu/PPFC nanocomposite thin ﬁlms were analyzed by X-ray photoelectron spectroscopy (XPS, SmartLab, Rigaku, Tokyo, Japan). AXIS Nova, Kratos, Manchester, UK) and X-ray diffraction (XRD, SmartLab, Rigaku, Tokyo, Japan). 3. Results 3. Results The Cu 20 and Cu 50 composite targets showed no electrical conductivity, while the Cu 80 The Cu 20 and Cu 50 composite targets showed no electrical conductivity, while the Cu 80 −3 targets showed a good sheet resistance of 2.1 10 W/sq. Therefore, ﬁrst, the nanocomposite thin targets showed a good sheet resistance of 2.1 × 10 Ω/sq. Therefore, first, the nanocomposite thin ﬁlm was fabricated using an RF power source, and the change in the physical properties of the thin film was fabricated using an RF power source, and the change in the physical properties of the thin ﬁlm according to the Cu composition in the composite target was investigated. Figure 2a shows a film according to the Cu composition in the composite target was investigated. Figure 2a shows a cross-sectional TEM image of the Cu 80 MF thin ﬁlm. The inserted element mapping image displays cross-sectional TEM image of the Cu 80 MF thin film. The inserted element mapping image displays homogenous distribution of copper and ﬂuorine atoms in the thin ﬁlm. Cu metal nanoclusters were homogenous distribution of copper and fluorine atoms in the thin film. Cu metal nanoclusters were distributed in a spherical shape with a size of 10–20 nm. Figure 2b shows a lattice of nanocluster Cu in distributed in a spherical shape with a size of 10–20 nm. Figure 2b shows a lattice of nanocluster Cu PPFC thin ﬁlm matrix. The central Cu nanocluster domain, which is marked yellow, shows (111) plane in PPFC thin film matrix. The central Cu nanocluster domain, which is marked yellow, shows (111) orientation with a lattice distance of 0.208 nm. In this TEM image, we conﬁrmed that Cu nanoclusters plane orientation with a lattice distance of 0.208 nm. In this TEM image, we confirmed that Cu were well formed as a crystalline phase in the plasma polymer ﬂuorocarbon matrix. nanoclusters were well formed as a crystalline phase in the plasma polymer fluorocarbon matrix. Figure 2. (a) Cross-sectional TEM image of the Cu 80 MF thin ﬁlm and element mapping images, Figure 2. (a) Cross-sectional TEM image of the Cu 80 MF thin film and element mapping images, (b) (b) nanocluster Cu in PPFC thin ﬁlm matrix. nanocluster Cu in PPFC thin film matrix. Figure 3 shows the optical properties for a 100 nm thick Cu/PPFC nanocomposite thin ﬁlm. Figure 3 shows the optical properties for a 100 nm thick Cu/PPFC nanocomposite thin film. Figure 3a shows the optical transmittance graph of the Cu/PPFC nanocomposite thin ﬁlm deposited Figure 3a shows the optical transmittance graph of the Cu/PPFC nanocomposite thin film deposited by RF sputtering. For comparison, the results for the thin ﬁlms deposited using a pure PTFE target by RF sputtering. For comparison, the results for the thin films deposited using a pure PTFE target devoid of Cu are also shown. The optical properties of the Cu 20 RF and Cu 50 RF nanocomposite devoid of Cu are also shown. The optical properties of the Cu 20 RF and Cu 50 RF nanocomposite thin ﬁlms were very similar to those of PTFE RF thin ﬁlms. They exhibited a high transmittance of thin films were very similar to those of PTFE RF thin films. They exhibited a high transmittance of 90% or more in the visible light region and showed excellent transmission characteristics even in the 90% or more in the visible light region and showed excellent transmission characteristics even in the infrared (IR) region. For the Cu 80 RF thin ﬁlm, visible light transmittance was drastically decreased, infrared (IR) region. For the Cu 80 RF thin film, visible light transmittance was drastically decreased, and the transmittance was about 70% at a wavelength of 500 nm. As the Cu content increased, the and the transmittance was about 70% at a wavelength of 500 nm. As the Cu content increased, the characteristics of Cu in the nanocomposite thin ﬁlm became more remarkable. Figure 3b shows the characteristics of Cu in the nanocomposite thin film became more remarkable. Figure 3b shows the optical transmittance characteristics of the nanocomposite thin ﬁlms deposited by RF, MF, and DC optical transmittance characteristics of the nanocomposite thin films deposited by RF, MF, and DC sputtering with a Cu 80 target, which has a low electrical resistance. The Cu 80 MF thin ﬁlm exhibited sputtering with a Cu 80 target, which has a low electrical resistance. The Cu 80 MF thin film a transmittance of less than 20% in the visible light region, whereas the Cu 80 DC thin ﬁlm had a exhibited a transmittance of less than 20% in the visible light region, whereas the Cu 80 DC thin film transmittance of less than 10%, which was similar to that of the Cu thin ﬁlm. Thus, the transmittance had a transmittance of less than 10%, which was similar to that of the Cu thin film. Thus, the is high in the order of Cu 80 RF > Cu 80 MF > Cu 80 DC, conﬁrming that the physical properties of the transmittance is high in the order of Cu 80 RF > Cu 80 MF > Cu 80 DC, confirming that the physical ﬁlms differ depending on the power source even when a composite target of the same composition properties of the films differ depending on the power source even when a composite target of the is used. Remarkably, the Cu 80 MF nanocomposite thin ﬁlm showed an electrical conductivity of same composition is used. Remarkably, the Cu 80 MF nanocomposite thin film showed an electrical 2 10 W/sq, whereas the electrical resistance of the Cu 80 DC thin ﬁlm was as low as 34.55 W/sq. conductivity of 2 × 10 Ω/sq, whereas the electrical resistance of the Cu 80 DC thin film was as low as Thus, the content and role of Cu in the nanocomposite thin ﬁlms fabricated using the MF and DC 34.55 Ω/sq. Thus, the content and role of Cu in the nanocomposite thin films fabricated using the MF power sources are greater than that in those obtained using RF. All other samples showed no electrical and DC power sources are greater than that in those obtained using RF. All other samples showed no electrical conductivity. Figure 3c plots the optical absorption of the Cu/PPFC nanocomposite thin films as a function of the target composition and power source. The Cu 80 MF nanocomposite thin Appl. Sci. 2019, 9, 1296 5 of 10 Appl. Sci. 2019, 9, x FOR PEER REVIEW 5 of 10 conductivity. Figure 3c plots the optical absorption of the Cu/PPFC nanocomposite thin ﬁlms as a function film exhiof bited the a tar n get abso composition rption peak and at 61 power 8 nm, sour wher ce. eaThe s tha Cu t fo 80 r th MF e Cu nanocomposite 80 DC thin fithin lm wa ﬁlm s at 6 exhibited 78 nm. an absorption peak at 618 nm, whereas that for the Cu 80 DC thin ﬁlm was at 678 nm. This is attributed This is attributed to the surface plasmon resonance phenomenon of the metal nanoclusters [1,2] and to con the firms surface that th plasmon e Cu narn esonance oclusters phenomenon are well formed of the in tmetal he PPFC nanoclusters matrix. It i [s 1,ex 2]pe and cted conﬁrms that the that size the of Cu nanoclusters are well formed in the PPFC matrix. It is expected that the size of the agglomeration the agglomeration of Cu nanoclusters in Cu 80 DC is larger than that in Cu 80 MF because the peak of poCu sitio nanoclust n is red ers shiin fted Cu . The 80 DC large is lar siger ze o than f the that Cu innCu ano 80 clust MF er because s also athe ffecpeak ts the position conducti is v red ity shifted. of the The nano lar coge mpo size site of th the in fCu ilms. nanoclusters Figure 3d coalso mpaaf refects s the the tranconductivity smittance and of co the lor nanocomposite of each sample. thin The PTFE ﬁlms. Figur RF, Cu e 3 2 d 0 compar RF, and es Cu the 50 transmittance RF nanocomand posite color thin of fieach lms a sample. re quite The tranPTFE spareRF nt ,aCu nd co 20lRF orl,ess. andHo Cu wev 50 RF er, nanocomposite the Cu 80 RF sam thin ple ﬁlms is sliar gh etl quite y yello transpar w, andent the and Cu colorless. 80 MF and However Cu 80 DC , the saCu mpl 80 es RF are sample red in is col slightly or and yellow exhibit l , and ow tra thenCu smi80 ttaMF nce.and Cu 80 DC samples are red in color and exhibit low transmittance. Figure 3. (a) Transmittance spectra in the wavelength range 300–2400 nm according to Cu content, Figure 3. (a) Transmittance spectra in the wavelength range 300–2400 nm according to Cu content, (b) transmittance spectra according to power sources using the Cu 80 target, (c) absorption spectra (b) transmittance spectra according to power sources using the Cu 80 target, (c) absorption spectra according to Cu content and power sources, and (d) photographs of the Cu/PPFC nanocomposite thin according to Cu content and power sources, and (d) photographs of the Cu/PPFC nanocomposite ﬁlms placed on a LED lamp. thin films placed on a LED lamp. The PTFE RF thin ﬁlm exhibited excellent water repellency owing to its low surface energy. The PTFE RF thin film exhibited excellent water repellency owing to its low surface energy. Figure 4 shows the water contact angle value of each sample for transmittance at 500 nm. The pure Figure 4 shows the water contact angle value of each sample for transmittance at 500 nm. The pure PTFE, Cu 20 RF, and Cu 50 RF thin ﬁlms showed almost similar transmittance, while their water PTFE, Cu 20 RF, and Cu 50 RF thin films showed almost similar transmittance, while their water contact angle decreased proportionally with increasing Cu content. This was because the amount of contact angle decreased proportionally with increasing Cu content. This was because the amount of Cu contained in the thin ﬁlm was so small that it did not affect the transmittance; however, the Cu Cu contained in the thin film was so small that it did not affect the transmittance; however, the Cu was distributed on the surface and therefore affected the surface energy. For different power sources, was distributed on the surface and therefore affected the surface energy. For different power the water contact angle decreased in the order Cu 80 RF > Cu 80 MF > Cu 80 DC, in the same order sources, the water contact angle decreased in the order Cu 80 RF > Cu 80 MF > Cu 80 DC, in the same as their transmittance. Table 1 summarizes the water contact angle, sheet resistance, transmittance at order as their transmittance. Table 1 summarizes the water contact angle, sheet resistance, 500 nm, and b* (yellow index) value of each sample. transmittance at 500 nm, and b* (yellow index) value of each sample. Appl. Sci. 2019, 9, 1296 6 of 10 Appl. Sci. 2019, 9, x FOR PEER REVIEW 6 of 10 Figure 4. Optical transmittance at 500 nm for different Cu contents and power sources. Figure 4. Optical transmittance at 500 nm for different Cu contents and power sources. Table 1. Properties of Cu/PPFC nanocomposite thin ﬁlms using Cu/PTFE composite targets. b*—yellow Table 1 index. . Properties of Cu/PPFC nanocomposite thin films using Cu/PTFE composite targets. b*—yellow index. Contact Angle Sheet Resistance Transmittance Target Power Type b* (deg.) (W/sq) (%) Power Contact Angle Sheet Resistance Transmittance Target b* Pure PTFE RF 109.83 0.42 over 90.56 0.27 0.69 0.06 Type (deg.) (Ω/sq) (%) Cu Pure 20/PTFE PTFE 80 RF RF 109 100.34 .83 ± 0.4 0.33 2 ov over er 9 89.92 0.56 ± 0 0.29 .27 1.31 0.69 ± 0.04 0.06 Cu 20/PTFE 80 RF 100.34 ± 0.33 over 89.92 ± 0.29 1.31 ± 0.04 Cu 50/PTFE 50 RF 95.85 0.44 over 89.49 0.32 1.37 0.04 Cu 50/PTFE 50 RF 95.85 ± 0.44 over 89.49 ± 0.32 1.37 ± 0.04 Cu 80/PTFE 20 RF 76.67 0.19 over 64.80 0.33 14.30 0.08 Cu 80/PTFE 20 RF 76.67 ± 0.19 over 4 64.80 ± 0.33 14.30 ± 0.08 Cu 80/PTFE 20 MF 12.10 0.48 2.00 0.21 (10 ) 15.68 0.21 22.39 0.15 Cu 80/PTFE 20 MF 12.10 ± 0.48 2.00 ± 0.21 (×10 ) 15.68 ± 0.21 22.39 ± 0.15 Cu 80/PTFE 20 DC 48.31 0.33 34.55 1.40 5.62 0.11 6.48 0.05 Cu 80/PTFE 20 DC 48.31 ± 0.33 34.55 ± 1.40 5.62 ± 0.11 6.48 ± 0.05 Figure 5a shows the XRD patterns of the Cu/PPFC nanocomposite thin ﬁlms prepared by RF Figure 5a shows the XRD patterns of the Cu/PPFC nanocomposite thin films prepared by RF sputtering. The XRD pattern of the PTFE RF thin ﬁlm shows a broad peak around 2 = 23 , implying sputtering. The XRD pattern of the PTFE RF thin film shows a broad peak around 2θ = 23°, implying that the thin ﬁlm is amorphous. Cu 20 RF also exhibited an amorphous state, indicating that the Cu that the thin film is amorphous. Cu 20 RF also exhibited an amorphous state, indicating that the Cu content is randomly distributed in the polymer matrix without forming clusters. The XRD patterns of content is randomly distributed in the polymer matrix without forming clusters. The XRD patterns the Cu 50 RF thin ﬁlms showed Bragg peaks attributed to the (200) crystal face of Cu at 2 50.6 . of the Cu 50 RF thin films showed Bragg peaks attributed to the (200) crystal face of Cu at 2θ ≈ 50.6°. These results are clear evidence that the Cu/PPFC nanocomposite is well formed. The Cu 80 RF These results are clear evidence that the Cu/PPFC nanocomposite is well formed. The Cu 80 RF thin thin ﬁlms showed Bragg peaks due to CuF and Cu O crystals. Considering that the Cu/PPFC 2 2 films showed Bragg peaks due to CuF2 and Cu2O crystals. Considering that the Cu/PPFC nanocomposite thin ﬁlm was fabricated in an argon atmosphere under vacuum, it is considered nanocomposite thin film was fabricated in an argon atmosphere under vacuum, it is considered that that the Cu O crystal peaks were due to the oxidation of Cu when the thin ﬁlm was exposed to air. the Cu2O crystal peaks were due to the oxidation of Cu when the thin film was exposed to air. Unexpectedly, Cu crystalline peaks were not observed in the Cu 80 RF thin ﬁlm. Figure 5b shows the Unexpectedly, Cu crystalline peaks were not observed in the Cu 80 RF thin film. Figure 5b shows the XRD patterns of the Cu 80 RF, MF, and DC nanocomposite thin ﬁlms. Unlike the Cu 80 RF thin ﬁlms, XRD patterns of the Cu 80 RF, MF, and DC nanocomposite thin films. Unlike the Cu 80 RF thin films, which only exhibit CuF and Cu O crystal phases, the XRD patterns of the Cu/PPFC nanocomposite 2 2 which only exhibit CuF2 and Cu2O crystal phases, the XRD patterns of the Cu/PPFC nanocomposite thin ﬁlms prepared by DC and MF sputtering show a Cu cubic crystal phase at 2 40.5 , Cu O cubic thin films prepared by DC and MF sputtering show a Cu cubic crystal phase at 2θ ≈ 40.5°, Cu 2O crystal phase at 2 36.6 , and CuCO monoclinic crystal phase at 2 25.8 [32,33]. The fraction cubic crystal phase at 2θ ≈ 36.6°, and CuCO3 monoclinic crystal phase at 2θ ≈ 25.8° [32,33]. The of the Cu crystal phase calculated from the XRD patterns of the Cu 80 MF and Cu 80 DC thin ﬁlms fraction of the Cu crystal phase calculated from the XRD patterns of the Cu 80 MF and Cu 80 DC thin was 14.2% and 21.1%, respectively, whereas that in the Cu 80 DC thin ﬁlms showed larger values. films was 14.2% and 21.1%, respectively, whereas that in the Cu 80 DC thin films showed larger The crystal size of the Cu 80 MF and Cu 80 DC thin ﬁlms, as calculated by the Debye–Scherrer equation values. The crystal size of the Cu 80 MF and Cu 80 DC thin films, as calculated by the Debye– (D = 0.916/ cos , D: Crystalline size, : X-ray wavelength, : Full width half-maximum (FWHM) of Scherrer equation (D = 0.916λ/βcos θ, D: Crystalline size, λ: X-ray wavelength, β: Full width Bragg peak, : Scattering angle), was about 5 nm [32]. half-maximum (FWHM) of Bragg peak, θ: Scattering angle), was about 5 nm [32]. Appl. Sci. 2019, 9, 1296 7 of 10 Appl. Sci. 2019, 9, x FOR PEER REVIEW 7 of 10 Figure 5. XRD patterns of (a) pure PTFE, Cu 20 RF, Cu 50 RF, Cu 80 RF, and (b) Cu 80 RF, Cu 80 MF, Figure 5. XRD patterns of (a) pure PTFE, Cu 20 RF, Cu 50 RF, Cu 80 RF, and (b) Cu 80 RF, Cu 80 MF, and Cu 80 DC nanocomposite thin ﬁlms. and Cu 80 DC nanocomposite thin films. The chemical structure of the Cu/PPFC nanocomposite thin ﬁlms was analyzed by XPS. The intensity The chemi ofca the l struc binding ture oener f the gy Cu/ was PPFC calibrated nanocom based posite on ththe in fil position ms was of ana the lyzed C–C by bond XPS. (sp The intensity of the binding energy was calibrated based on the position of the C–C bond (sp hybrid hybrid orbital, 284.8 eV). Figure 6a shows the normalized C 1s core-level XPS spectra of the Cu/PPFC nanocomposite orbital, 284.8 eV thin ). Fiﬁlms gure pr 6aepar shoed ws by the RF no sputtering rmalized C of1the s co Cu/PTFE re-level Xcomposite PS spectra tar of get. the The Cu/PP C FC 1s nanocomposite thin films prepared by RF sputtering of the Cu/PTFE composite target. The C 1s spectra exhibit broad Gaussian deconvolution peaks that have the following customary assignments for spec a tra ﬂuor exhi ocarbon bit brothin ad Gﬁlm: aussia 294.0 n dec eV onv (CF oluti ),o 292.0 n peaeV ks t(CF hat ha ), 289.8 ve theeV foll (CF), owin287.5 g custo eV m(C–CF ary assi), gn and ment an s 3 2 n for a fluorocarbon thin film: 294.0 eV (CF3), 292.0 eV (CF2), 289.8 eV (CF), 287.5 eV (C–CFn), and an additional C=O peak at 288.6 eV owing to binding with oxygen [16,31,34]. The intensity of the CF bond, additio which nal C= is O typical peak ain t 28 a8ﬂuor .6 eV ocarbon owing to thin bin ﬁlm, ding is wi decr th o eased xygenowing [16,31,to 34] the . The low inﬂuorine tensity obonding f the CF2 bond, which is typical in a fluorocarbon thin film, is decreased owing to the low fluorine bonding ratio and high carbon bonding ratio in the thin ﬁlm with increasing Cu content. In the Cu 80 RF thin ﬁlm, ratio the and composition high carbonratio bond of inﬂuorine g ratio in was the drastically thin film wi decr th ieased, ncreasi and ng C most u con of tent. the Ibonds n the Cu wer 8e 0 formed RF thin film, the composition ratio of fluorine was drastically decreased, and most of the bonds were formed between carbon and oxygen (C=O) upon exposure of the thin ﬁlm to air. In the Cu 80 RF thin ﬁlm, the betwee bonding n carb ratio on an of d ﬂuorine oxygen (decr C=O) eased uponsharply exposure , and of the the bond thin fibetwe lm to en air.carbon In the Cu and8oxygen 0 RF thin (C=O) film, the bonding ratio of fluorine decreased sharply, and the bond between carbon and oxygen (C=O) appeared after air exposure of the thin ﬁlm. Figure 6b shows that the C 1s core-level spectra of the Cu 80 appe RFa , re Cu d 80 after MF a,ir and expo Cu sur 80 e DC of th thin e thﬁlms in film have . Figure no binding 6b show ener s thgy at th peaks e C 1due s core to-l the evel CF spec bond, tra ofand the Cu 80 RF, Cu 80 MF, and Cu 80 DC thin films have no binding energy peaks due to the CF 2 bond, that the carbon bond is dominant. The Cu 2p spectra of the Cu/PPFC nanocomposite thin ﬁlms are shown and tha in t th Figur e car eb6 oc. n b The ond Cu is 20 dom RF inand ant. Cu The 50 Cu RF 2p thin spec ﬁlms tra oshowed f the Cu/almost PPFC n no ano binding composi ener te th gy in peak, films are shown in Figure 6c. The Cu 20 RF and Cu 50 RF thin films showed almost no binding energy whereas the Cu 80 RF, Cu 80 MF, and Cu 80 DC thin ﬁlms showed Cu 2p binding energy peaks 3/2 at pe932.7 ak, wh eV ere and as th ae Cu Cu2p 80 RF, binding Cu 80 ener MF, gy and peak Cu at 80 952.6 DC th eV in ( fD ilm BE s = sh19.9 owed eV) Cu [12 2p ]. 3/2In bithe ndin Cu g e80 ner RF gy 1/2 peaks at 932.7 eV and a Cu 2p1/2 binding energy peak at 952.6 eV (ΔBE = 19.9 eV) [12]. In the Cu 80 RF thin ﬁlm, CuCO binding energy peaks were observed at 934.6 eV (Cu 2p ) and 954.5 eV (Cu 2p ), 3 3/2 3/2 which thin filis mpr , CuC esumably O3 bind due ing to en surfac ergy pe e oxidation aks were o after bserthin ved a ﬁlm t 93fabrication. 4.6 eV (Cu 2A p3/2 shake-up ) and 954satellite .5 eV (Cu peak 2p3/2 of ), 2+ 9 which is presumably due to surface oxidation after thin film fabrication. A shake-up satellite peak of Cu [Ar] 3d orbital conﬁguration was observed in the binding energy range of 938.5–946.0 eV (Cu 2+ 9 2p Cu ) [A and r] 3959.0–965 d orbital co eV nf(Cu igura 2p tion ). wShake-up as observed satellite in the peaks bindin appear g energy str r ongly ange o when f 938.Cu 5–94 is 6.oxidized 0 eV (Cu 3/2 1/2 2p3/2) and 959.0–965 eV (Cu 2p1/2). Shake-up satellite peaks appear strongly when Cu is oxidized to to form CuO or CuF . Thus, the Cu 80 DC thin ﬁlm exhibits excellent conductivity, a large crystal form CuO or CuF2. Thus, the Cu 80 DC thin film exhibits excellent conductivity, a large crystal size size of Cu, as well as a low oxidation degree. Figure 6d shows the chemical quantiﬁcation results, of Cu, as well as a low oxidation degree. Figure 6d shows the chemical quantification results, obtained by considering the relative sensitivity factors of each binding energy peak in the XPS spectra. obtained by considering the relative sensitivity factors of each binding energy peak in the XPS As the weight ratio of Cu increases from Cu 20 wt.% (9.12 mol%) to 50 wt.% (20.8 mol%) and 80 spectra. As the weight ratio of Cu increases from Cu 20 wt.% (9.12 mol%) to 50 wt.% (20.8 mol%) wt.% (51.2 mol%) in the Cu/PTFE composite target, the dramatic change in the physical properties and 80 wt.% (51.2 mol%) in the Cu/PTFE composite target, the dramatic change in the physical of the Cu/PPFC nanocomposite thin ﬁlm is attributed to the difference in the quantitative ratio of properties of the Cu/PPFC nanocomposite thin film is attributed to the difference in the quantitative copper atoms and ﬂuorine atoms in the Cu/PPFC nanocomposite thin ﬁlm. Cu concentration of the ratio of copper atoms and fluorine atoms in the Cu/PPFC nanocomposite thin film. Cu concentration nanocomposite thin ﬁlms Cu 20 RF (0.10%), Cu 50 RF (0.27%), and Cu 80 RF (6.51%) were different of the nanocomposite thin films Cu 20 RF (0.10%), Cu 50 RF (0.27%), and Cu 80 RF (6.51%) were from the composite targets but also gradually increased. different from the composite targets but also gradually increased. Appl. Sci. 2019, 9, 1296 8 of 10 Appl. Sci. 2019, 9, x FOR PEER REVIEW 8 of 10 Figure 6. Normalized XPS spectra of (a) C 1s with increasing Cu content, (b) C 1s with RF, MF, and DC Figure 6. Normalized XPS spectra of (a) C 1s with increasing Cu content, (b) C 1s with RF, MF, and power sources, and (c) Cu 2p for the Cu/PPFC nanocomposite thin ﬁlms with varying Cu contents DC power sources, and (c) Cu 2p for the Cu/PPFC nanocomposite thin films with varying Cu and power sources. (d) Calculated carbon, ﬂuorine, and copper ratio for the nanocomposite Cu/PPFC contents and power sources. (d) Calculated carbon, fluorine, and copper ratio for the nanocomposite nanocomposite thin ﬁlms. Cu/PPFC nanocomposite thin films. 4. Conclusions 4. Conclusions In summary, we have successfully fabricated Cu/PTFE composite targets with various Cu weight In summary, we have successfully fabricated Cu/PTFE composite targets with various Cu percentages for sputtering and deposited Cu/PPFC nanocomposite thin ﬁlms. This was followed by weight percentages for sputtering and deposited Cu/PPFC nanocomposite thin films. This was analysis of the properties of the Cu/PPFC nanocomposite thin ﬁlms with respect to the Cu composition followed by analysis of the properties of the Cu/PPFC nanocomposite thin films with respect to the ratio. The Cu nanoclusters were well distributed in a spherical shape with a size of 10–20 nm examined Cu composition ratio. The Cu nanoclusters were well distributed in a spherical shape with a size of by a FE-TEM image. The Cu/PPFC nanocomposite ﬁlms prepared by RF sputtering with Cu 20 and 50 10–20 nm examined by a FE-TEM image. The Cu/PPFC nanocomposite films prepared by RF targets showed very similar transmittance and color characteristics to those of pure PTFE. However, sputtering with Cu 20 and 50 targets showed very similar transmittance and color characteristics to the water contact angle gradually decreased owing to the Cu on the ﬁlm surface. The effect of Cu those of pure PTFE. However, the water contact angle gradually decreased owing to the Cu on the content was more pronounced in the Cu 80 target. The Cu 80 target has excellent conductivity and can film surface. The effect of Cu content was more pronounced in the Cu 80 target. The Cu 80 target has be sputtered not only in RF but also in MF and DC power sources; moreover, the physical properties excellent conductivity and can be sputtered not only in RF but also in MF and DC power sources; of the thin ﬁlm change signiﬁcantly depending on the power source. Interestingly, the Cu 80 MF moreover, the physical properties of the thin film change significantly depending on the power and Cu 80 DC thin ﬁlms exhibited absorption peaks at 618 and 678 nm, respectively, indicating that source. Interestingly, the Cu 80 MF and Cu 80 DC thin films exhibited absorption peaks at 618 and the Cu nanoclusters were well formed. Further, from the red shift of the absorption peak, it can be 678 nm, respectively, indicating that the Cu nanoclusters were well formed. Further, from the red assumed that the size of the nanoclusters prepared using DC was larger than that using MF, which is shift of the absorption peak, it can be assumed that the size of the nanoclusters prepared using DC also why the nanocomposite ﬁlms prepared by MF and DC exhibit sheet resistances of 2 10 and was larger than that using MF, which is also why the nanocomposite films prepared by MF and DC 34.55 W/sq, respectively, thus explaining why the electrical properties of the thin ﬁlms prepared using exhibit sheet resistances of 2 × 10 and 34.55 Ω/sq, respectively, thus explaining why the electrical DC are superior. properties of the thin films prepared using DC are superior. This study describes a novel method to fabricate metal–polymer nanocomposites. This method This study describes a novel method to fabricate metal–polymer nanocomposites. This method can be expanded and diversiﬁed to easily fabricate not only various metal nanocomposites but also can be expanded and diversified to easily fabricate not only various metal nanocomposites but also ceramics and semiconductor nanocomposites. Therefore, this method is industrially promising, as it enables fabrication over a large area and in a continuous manner. Appl. Sci. 2019, 9, 1296 9 of 10 ceramics and semiconductor nanocomposites. Therefore, this method is industrially promising, as it enables fabrication over a large area and in a continuous manner. Author Contributions: S.-J.L. designed the study and the experiments. S.H.K. fabricated the Cu/PPFC thin ﬁlms using a test sputter system. S.H.K., M.K., and J.S.P. analyzed the properties of the Cu/PPFC thin ﬁlms. S.-J.L. and M.K. wrote the manuscript. All of the authors discussed the results and commented on the manuscript. 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This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Applied Sciences Multidisciplinary Digital Publishing Institute http://www.deepdyve.com/lp/multidisciplinary-digital-publishing-institute/optical-electrical-and-surface-properties-of-cu-plasma-polymer-c6jwssr3d6

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Controlled syntheses of Ag–polytetrafluoroethylene nanocomposite thin films by co-sputtering from two magnetron sources
Nanotechnology, 16
A. Biswas, O. Aktas, U. Schürmann, U. Saeed, V. Zaporojtchenko, F. Faupel, T. Strunskus (2004)
Tunable multiple plasmon resonance wavelengths response from multicomponent polymer-metal nanocomposite systems
Applied Physics Letters, 84

Publisher: Multidisciplinary Digital Publishing Institute
Copyright: © 1996-2019 MDPI (Basel, Switzerland) unless otherwise stated
ISSN: 2076-3417
DOI: 10.3390/app9071296
Publisher site: See Article on Publisher Site

Abstract

applied sciences Article Optical, Electrical, and Surface Properties of Cu/Plasma Polymer Fluorocarbon Nanocomposite Thin Film Fabricated Using Metal/Polymer Composite Target Sung Hyun Kim, Mac Kim, Jae Seong Park and Sang-Jin Lee * Chemical Materials Solutions Center, Korea Research Institute of Chemical Technology, Daejeon 34114, Korea; wdy1332@krict.re.kr (S.H.K.); kimmac79@krict.re.kr (M.K.); jspark@krict.re.kr (J.S.P.) * Correspondence: leesj@krict.re.kr; Tel.: +82-42-860-7902, Fax.: +82-42-860-7909 Received: 27 February 2019; Accepted: 26 March 2019; Published: 28 March 2019 Abstract: We propose a new method of fabricating metal–polymer composite targets for sputtering, which makes it easier to control the composition and enables the homogeneous and reproducible fabrication of metal–polymer nanocomposites over large areas. Using Cu/polytetraﬂuoroethylene composite targets containing 20, 50, and 80 wt.% Cu, Cu/plasma polymer ﬂuorocarbon (PPFC) nanocomposite thin ﬁlms were prepared by radio-frequency (RF) sputtering. Targets with 80 wt.% Cu were conductive; moreover, sputtering was possible not only with RF but also with mid-range frequency (MF) and direct current (DC) power sources. The nanocomposite thin ﬁlm deposited by MF and DC power using an 80 wt.% Cu target showed near-metallic characteristics, exhibited absorption peaks at 618 and 678 nm, and had a surface resistance of 2 10 and 34.55 W/sq, respectively. We also analyzed the structure and composition of the Cu/PPFC nanocomposite ﬁlms by X-ray diffraction and X-ray photoelectron spectroscopy. The described metal–polymer targets can advance the applications and commercialization of nanocomposite thin ﬁlms. Keywords: Cu/polytetraﬂuoroethylene composite target; plasma polymer ﬂuorocarbon; nanocomposite thin ﬁlm; sputtering power source; surface plasmon resonance 1. Introduction Polymer–metal nanocomposites exhibit excellent optical [1–8], electrical [1,4], and mechanical properties [9,10] and have been attracting much attention owing to their various characteristics such as surface hardness [6], bioactivity [11,12], perfect absorbance, [13–15], and sensing ability [16]. Polymers with good insulating properties are well suited as host materials for supporting a variety of metal clusters [5,17]. The excellent properties of polymer–metal nanocomposites depend on the size, quantity, and shape of various metal clusters contained in the polymer matrix; various studies elucidating these properties have been performed [17,18], with reference to surface antimicrobials and abrasion-resistant coatings, and gas sensor ﬁlms [19–22]. As a polymer matrix, polytetraﬂuoroethylene (PTFE), which is mechanically, thermally, and chemically stable, and has excellent insulation and optical properties, is widely used [1,3,6,9,11,19,23]. Studies using noble metals such as Ag [5,9,11,19,24–26], Au [3,16,27], and Cu [12–14] have been carried out, but mostly, Ag and Au have been used. In addition to noble metals, nanocomposites using SiO [6], graphite [10], ZnO [19], Ti [28], Fe–Ni–Co [29], and TiO [30], with PTFE, have also been reported. A nanocomposite can be fabricated by the physical vapor deposition (PVD) method, as PVD allows for control of the dopant, enables uniform coating, and minimizes the reaction with air. The co-sputtering method employing two sputtering cathodes [3,6,9,10,12–14,19,28] is the Appl. Sci. 2019, 9, 1296; doi:10.3390/app9071296 www.mdpi.com/journal/applsci Appl. Sci. 2019, 9, 1296 2 of 10 most widely used method, and other methods involve the use of an evaporator [9,25], sputter evaporator, ion beam co-sputtering [16], and pulsed laser deposition [24], to fabricate a polymer–metal nanocomposite. However, the use of two sputtering cathodes or a combination of two deposition methods to fabricate nanocomposites requires precise control for yield matching; moreover, it is difﬁcult to ensure reproducibility of the experimental results owing to the complicated equipment conﬁguration and difﬁculty in securing uniformity over a large area, which are stumbling blocks toward commercialization. In a previous study, our group found that a plasma polymer ﬂuorocarbon (PPFC) thin ﬁlm prepared using a carbon nanotube (CNT)/PTFE composite sputtering target exhibited diverse physical properties depending on the content of the CNT. In addition, it has been reported that CNT, when added to a composite target, imparts conductivity; hence, sputtering is also possible using a mid-range frequency (MF) power source [31]. Taking our previous study forward, in this study, a Cu/PTFE composite target for sputtering was ﬁrst introduced for fabricating a Cu/PPFC nanocomposite thin ﬁlm by uniformly dispersing Cu metal powder in PTFE powder and pressing at high temperature. Previously, the composite target was prepared by attaching half of the polymer target to half of the metal target, or attaching a metal foil or wire to the surface of the polymer target [1,6]. However, in those studies, it was challenging to deposit a nanocomposite thin ﬁlm of uniform composition ratio over a large substrate area and prepare a reproducible target; therefore, practical composite targets have been difﬁcult to achieve thus far. We fabricated noble polymer–metal composite targets with 20, 50, and 80 wt.% Cu in PTFE powder. Thus, the ﬁlling ratio of the metal nanoclusters in the nanocomposite thin ﬁlm can be easily controlled, and the nanocomposite thin ﬁlm can be prepared by long-duration sputtering with one target in the same manner as the conventional sputtering target, enabling excellent reproducibility. Finally, because of the controllability and simple equipment conﬁguration, large-area sputtering is possible; hence, this method can be employed in a wide variety of polymer–metal nanocomposite technical and commercial applications. In this study, we investigated the physical and chemical properties of the Cu/PPFC nanocomposite thin ﬁlms with various Cu contents, and analyzed how the properties of the ﬁlms change with radio-frequency (RF), MF, and direct current (DC) power sources using the Cu/PTFE (20:80, w/w) target. 2. Materials and Methods 2.1. Preparation of Cu/PTFE Composite Sputtering Targets Cu powder (e-Cu25, Chang Sung) was mixed with PTFE powder (A7, DuPont) at weight ratios of 20:80, 50:50, and 80:20, respectively, following which composite sputtering Cu/PTFE targets were prepared by a high-temperature compression molding method. Compression pressure was 200 kgf/cm and molding temperature was 370 C. A pure PTFE sputtering target devoid of any Cu powder was also prepared by the same method for reference. Disk-type Cu/PTFE composite sputtering targets with a diameter of 10.16 cm and thickness of 0.64 cm were then fabricated by milling. For simplicity, the targets were labeled PTFE (Cu 0), Cu 20, Cu 50, and Cu 80 according to the composition ratio. Figure 1a sequentially shows the fabrication of the Cu/PTFE composite target. Appl. Sci. 2019, 9, 1296 3 of 10 Appl. Sci. 2019, 9, x FOR PEER REVIEW 3 of 10 Figure 1. (a) Sequential diagram of the fabrication of Cu/PTFE composite target. (b) Illustration of the Figure 1. (a) Sequential diagram of the fabrication of Cu/PTFE composite target. (b) Illustration of the sputtering process to deposit Cu/plasma polymer ﬂuorocarbon (PPFC) nanocomposite thin ﬁlms with sputtering process to deposit Cu/plasma polymer fluorocarbon (PPFC) nanocomposite thin films radio frequency (RF), mid-range frequency (MF), and direct current (DC) power sources. with radio frequency (RF), mid-range frequency (MF), and direct current (DC) power sources. 2.2. Fabrication of Cu/PPFC Nanocomposite Thin Films 2.2. Fabrication of Cu/PPFC Nanocomposite Thin Films The sputtering chamber was evacuated to a base pressure of 6.6 10 Pa by a mechanical pump −3 The sputtering chamber was evacuated to a base pressure of 6.6 × 10 Pa by a mechanical pump and a cryogenic pump. The partial pressure of Ar during the process was 0.93 Pa. The Cu/PPFC and a cryogenic pump. The partial pressure of Ar during the process was 0.93 Pa. The Cu/PPFC nanocomposite thin ﬁlms were fabricated using RF (13.56 MHz), MF (40 kHz), and DC power with a nanocomposite thin films were fabricated using RF (13.56 MHz), MF (40 kHz), and DC power with a sputtering power density of 1.23 W/cm . Dual magnetron cathodes were used for MF sputtering to sputtering power density of 1.23 W/cm . Dual magnetron cathodes were used for MF sputtering to improve sputtering efﬁciency. Target-to-substrate distance was ﬁxed at 24 cm. A schematic diagram improve sputtering efficiency. Target-to-substrate distance was fixed at 24 cm. A schematic diagram of the sputtering process for each power source is shown in Figure 1b. We used a polyethylene of the sputtering process for each power source is shown in Figure 1b. We used a polyethylene terephthalate (PET, KIMOTO, Japan) ﬁlm substrate of size 20 20 cm and thickness 125 m. In order terephthalate (PET, KIMOTO, Japan) film substrate of size 20 × 20 cm and thickness 125 μm. In to compare the physical properties of the thin ﬁlms with different Cu composition ratios, pure PTFE, order to compare the physical properties of the thin films with different Cu composition ratios, pure Cu 20, Cu 50, and Cu 80 composite targets were sputtered with an RF power source to fabricate the PTFE, Cu 20, Cu 50, and Cu 80 composite targets were sputtered with an RF power source to thin ﬁlms. Deposition rates for each composite target and sputtering power source were determined fabricate the thin films. Deposition rates for each composite target and sputtering power source were by using the Alpha step method (Dektak XT, Bruker, MA, USA). A thickness step is generated by determined by using the Alpha step method (Dektak XT, Bruker, MA, USA). A thickness step is covering a part of the sample for measurement. To investigate the physical properties of the Cu/PPFC generated by covering a part of the sample for measurement. To investigate the physical properties nanocomposite thin ﬁlms according to power source, 100 nm thin ﬁlms were fabricated by sputtering of the Cu/PPFC nanocomposite thin films according to power source, 100 nm thin films were with RF, MF, and DC power sources using the Cu 80 composite target. The fabricated thin ﬁlms were fabricated by sputtering with RF, MF, and DC power sources using the Cu 80 composite target. The named “target name + power source type” for clarity and conciseness. For example, a thin ﬁlm made fabricated thin films were named “target name + power source type” for clarity and conciseness. For by an RF power source using a Cu 20 composite target is named “Cu 20 RF”, whereas that made by a example, a thin film made by an RF power source using a Cu 20 composite target is named “Cu 20 DC power source using a Cu 80 composite target is named “Cu 80 DC”. RF”, whereas that made by a DC power source using a Cu 80 composite target is named “Cu 80 DC”. 2.3. Characterization of Cu/PPFC Nanocomposite Thin Films 2.3. Characterization of Cu/PPFC Nanocomposite Thin Films The nanocomposite structure of Cu/PPFC thin ﬁlm was investigated by ﬁeld-emission The nanocomposite structure of Cu/PPFC thin film was investigated by field-emission transmission electron microscopy (FE-TEM, Tecnai G2 F30 S-Twin, FEI Co., Hillsboro, OR, USA). transmission electron microscopy (FE-TEM, Tecnai G2 F30 S-Twin, FEI Co., Hillsboro, OR, USA). Optical properties of the thin ﬁlms were measured by UV–VIS spectroscopy (U-4100, Hitachi, Tokyo, Optical properties of the thin films were measured by UV–VIS spectroscopy (U-4100, Hitachi, Japan). Standard deviation of water contact angle, sheet resistance, optical transmittance, and b* Tokyo, Japan). Standard deviation of water contact angle, sheet resistance, optical transmittance, (yellow index) were measured by ﬁve points at each sample. The measuring points were the center and b* (yellow index) were measured by five points at each sample. The measuring points were the and four sides of the ﬁlm. The surface energy of the nanocomposite thin ﬁlm was measured using a center and four sides of the film. The surface energy of the nanocomposite thin film was measured contact angle analyzer (Phoenix 300 Touch, Surface Electro Optics, Suwon, Korea). The volume of water using a contact angle analyzer (Phoenix 300 Touch, Surface Electro Optics, Suwon, Korea). The droplets was 2 L, and the images were automatically analyzed by the system. Structural characteristics volume of water droplets was 2 μL, and the images were automatically analyzed by the system. Structural characteristics of the Cu/PPFC nanocomposite thin films were analyzed by X-ray Appl. Sci. 2019, 9, 1296 4 of 10 Appl. Sci. 2019, 9, x FOR PEER REVIEW 4 of 10 photoelectron spectroscopy (XPS, AXIS Nova, Kratos, Manchester, UK) and X-ray diffraction (XRD, of the Cu/PPFC nanocomposite thin ﬁlms were analyzed by X-ray photoelectron spectroscopy (XPS, SmartLab, Rigaku, Tokyo, Japan). AXIS Nova, Kratos, Manchester, UK) and X-ray diffraction (XRD, SmartLab, Rigaku, Tokyo, Japan). 3. Results 3. Results The Cu 20 and Cu 50 composite targets showed no electrical conductivity, while the Cu 80 The Cu 20 and Cu 50 composite targets showed no electrical conductivity, while the Cu 80 −3 targets showed a good sheet resistance of 2.1 10 W/sq. Therefore, ﬁrst, the nanocomposite thin targets showed a good sheet resistance of 2.1 × 10 Ω/sq. Therefore, first, the nanocomposite thin ﬁlm was fabricated using an RF power source, and the change in the physical properties of the thin film was fabricated using an RF power source, and the change in the physical properties of the thin ﬁlm according to the Cu composition in the composite target was investigated. Figure 2a shows a film according to the Cu composition in the composite target was investigated. Figure 2a shows a cross-sectional TEM image of the Cu 80 MF thin ﬁlm. The inserted element mapping image displays cross-sectional TEM image of the Cu 80 MF thin film. The inserted element mapping image displays homogenous distribution of copper and ﬂuorine atoms in the thin ﬁlm. Cu metal nanoclusters were homogenous distribution of copper and fluorine atoms in the thin film. Cu metal nanoclusters were distributed in a spherical shape with a size of 10–20 nm. Figure 2b shows a lattice of nanocluster Cu in distributed in a spherical shape with a size of 10–20 nm. Figure 2b shows a lattice of nanocluster Cu PPFC thin ﬁlm matrix. The central Cu nanocluster domain, which is marked yellow, shows (111) plane in PPFC thin film matrix. The central Cu nanocluster domain, which is marked yellow, shows (111) orientation with a lattice distance of 0.208 nm. In this TEM image, we conﬁrmed that Cu nanoclusters plane orientation with a lattice distance of 0.208 nm. In this TEM image, we confirmed that Cu were well formed as a crystalline phase in the plasma polymer ﬂuorocarbon matrix. nanoclusters were well formed as a crystalline phase in the plasma polymer fluorocarbon matrix. Figure 2. (a) Cross-sectional TEM image of the Cu 80 MF thin ﬁlm and element mapping images, Figure 2. (a) Cross-sectional TEM image of the Cu 80 MF thin film and element mapping images, (b) (b) nanocluster Cu in PPFC thin ﬁlm matrix. nanocluster Cu in PPFC thin film matrix. Figure 3 shows the optical properties for a 100 nm thick Cu/PPFC nanocomposite thin ﬁlm. Figure 3 shows the optical properties for a 100 nm thick Cu/PPFC nanocomposite thin film. Figure 3a shows the optical transmittance graph of the Cu/PPFC nanocomposite thin ﬁlm deposited Figure 3a shows the optical transmittance graph of the Cu/PPFC nanocomposite thin film deposited by RF sputtering. For comparison, the results for the thin ﬁlms deposited using a pure PTFE target by RF sputtering. For comparison, the results for the thin films deposited using a pure PTFE target devoid of Cu are also shown. The optical properties of the Cu 20 RF and Cu 50 RF nanocomposite devoid of Cu are also shown. The optical properties of the Cu 20 RF and Cu 50 RF nanocomposite thin ﬁlms were very similar to those of PTFE RF thin ﬁlms. They exhibited a high transmittance of thin films were very similar to those of PTFE RF thin films. They exhibited a high transmittance of 90% or more in the visible light region and showed excellent transmission characteristics even in the 90% or more in the visible light region and showed excellent transmission characteristics even in the infrared (IR) region. For the Cu 80 RF thin ﬁlm, visible light transmittance was drastically decreased, infrared (IR) region. For the Cu 80 RF thin film, visible light transmittance was drastically decreased, and the transmittance was about 70% at a wavelength of 500 nm. As the Cu content increased, the and the transmittance was about 70% at a wavelength of 500 nm. As the Cu content increased, the characteristics of Cu in the nanocomposite thin ﬁlm became more remarkable. Figure 3b shows the characteristics of Cu in the nanocomposite thin film became more remarkable. Figure 3b shows the optical transmittance characteristics of the nanocomposite thin ﬁlms deposited by RF, MF, and DC optical transmittance characteristics of the nanocomposite thin films deposited by RF, MF, and DC sputtering with a Cu 80 target, which has a low electrical resistance. The Cu 80 MF thin ﬁlm exhibited sputtering with a Cu 80 target, which has a low electrical resistance. The Cu 80 MF thin film a transmittance of less than 20% in the visible light region, whereas the Cu 80 DC thin ﬁlm had a exhibited a transmittance of less than 20% in the visible light region, whereas the Cu 80 DC thin film transmittance of less than 10%, which was similar to that of the Cu thin ﬁlm. Thus, the transmittance had a transmittance of less than 10%, which was similar to that of the Cu thin film. Thus, the is high in the order of Cu 80 RF > Cu 80 MF > Cu 80 DC, conﬁrming that the physical properties of the transmittance is high in the order of Cu 80 RF > Cu 80 MF > Cu 80 DC, confirming that the physical ﬁlms differ depending on the power source even when a composite target of the same composition properties of the films differ depending on the power source even when a composite target of the is used. Remarkably, the Cu 80 MF nanocomposite thin ﬁlm showed an electrical conductivity of same composition is used. Remarkably, the Cu 80 MF nanocomposite thin film showed an electrical 2 10 W/sq, whereas the electrical resistance of the Cu 80 DC thin ﬁlm was as low as 34.55 W/sq. conductivity of 2 × 10 Ω/sq, whereas the electrical resistance of the Cu 80 DC thin film was as low as Thus, the content and role of Cu in the nanocomposite thin ﬁlms fabricated using the MF and DC 34.55 Ω/sq. Thus, the content and role of Cu in the nanocomposite thin films fabricated using the MF power sources are greater than that in those obtained using RF. All other samples showed no electrical and DC power sources are greater than that in those obtained using RF. All other samples showed no electrical conductivity. Figure 3c plots the optical absorption of the Cu/PPFC nanocomposite thin films as a function of the target composition and power source. The Cu 80 MF nanocomposite thin Appl. Sci. 2019, 9, 1296 5 of 10 Appl. Sci. 2019, 9, x FOR PEER REVIEW 5 of 10 conductivity. Figure 3c plots the optical absorption of the Cu/PPFC nanocomposite thin ﬁlms as a function film exhiof bited the a tar n get abso composition rption peak and at 61 power 8 nm, sour wher ce. eaThe s tha Cu t fo 80 r th MF e Cu nanocomposite 80 DC thin fithin lm wa ﬁlm s at 6 exhibited 78 nm. an absorption peak at 618 nm, whereas that for the Cu 80 DC thin ﬁlm was at 678 nm. This is attributed This is attributed to the surface plasmon resonance phenomenon of the metal nanoclusters [1,2] and to con the firms surface that th plasmon e Cu narn esonance oclusters phenomenon are well formed of the in tmetal he PPFC nanoclusters matrix. It i [s 1,ex 2]pe and cted conﬁrms that the that size the of Cu nanoclusters are well formed in the PPFC matrix. It is expected that the size of the agglomeration the agglomeration of Cu nanoclusters in Cu 80 DC is larger than that in Cu 80 MF because the peak of poCu sitio nanoclust n is red ers shiin fted Cu . The 80 DC large is lar siger ze o than f the that Cu innCu ano 80 clust MF er because s also athe ffecpeak ts the position conducti is v red ity shifted. of the The nano lar coge mpo size site of th the in fCu ilms. nanoclusters Figure 3d coalso mpaaf refects s the the tranconductivity smittance and of co the lor nanocomposite of each sample. thin The PTFE ﬁlms. Figur RF, Cu e 3 2 d 0 compar RF, and es Cu the 50 transmittance RF nanocomand posite color thin of fieach lms a sample. re quite The tranPTFE spareRF nt ,aCu nd co 20lRF orl,ess. andHo Cu wev 50 RF er, nanocomposite the Cu 80 RF sam thin ple ﬁlms is sliar gh etl quite y yello transpar w, andent the and Cu colorless. 80 MF and However Cu 80 DC , the saCu mpl 80 es RF are sample red in is col slightly or and yellow exhibit l , and ow tra thenCu smi80 ttaMF nce.and Cu 80 DC samples are red in color and exhibit low transmittance. Figure 3. (a) Transmittance spectra in the wavelength range 300–2400 nm according to Cu content, Figure 3. (a) Transmittance spectra in the wavelength range 300–2400 nm according to Cu content, (b) transmittance spectra according to power sources using the Cu 80 target, (c) absorption spectra (b) transmittance spectra according to power sources using the Cu 80 target, (c) absorption spectra according to Cu content and power sources, and (d) photographs of the Cu/PPFC nanocomposite thin according to Cu content and power sources, and (d) photographs of the Cu/PPFC nanocomposite ﬁlms placed on a LED lamp. thin films placed on a LED lamp. The PTFE RF thin ﬁlm exhibited excellent water repellency owing to its low surface energy. The PTFE RF thin film exhibited excellent water repellency owing to its low surface energy. Figure 4 shows the water contact angle value of each sample for transmittance at 500 nm. The pure Figure 4 shows the water contact angle value of each sample for transmittance at 500 nm. The pure PTFE, Cu 20 RF, and Cu 50 RF thin ﬁlms showed almost similar transmittance, while their water PTFE, Cu 20 RF, and Cu 50 RF thin films showed almost similar transmittance, while their water contact angle decreased proportionally with increasing Cu content. This was because the amount of contact angle decreased proportionally with increasing Cu content. This was because the amount of Cu contained in the thin ﬁlm was so small that it did not affect the transmittance; however, the Cu Cu contained in the thin film was so small that it did not affect the transmittance; however, the Cu was distributed on the surface and therefore affected the surface energy. For different power sources, was distributed on the surface and therefore affected the surface energy. For different power the water contact angle decreased in the order Cu 80 RF > Cu 80 MF > Cu 80 DC, in the same order sources, the water contact angle decreased in the order Cu 80 RF > Cu 80 MF > Cu 80 DC, in the same as their transmittance. Table 1 summarizes the water contact angle, sheet resistance, transmittance at order as their transmittance. Table 1 summarizes the water contact angle, sheet resistance, 500 nm, and b* (yellow index) value of each sample. transmittance at 500 nm, and b* (yellow index) value of each sample. Appl. Sci. 2019, 9, 1296 6 of 10 Appl. Sci. 2019, 9, x FOR PEER REVIEW 6 of 10 Figure 4. Optical transmittance at 500 nm for different Cu contents and power sources. Figure 4. Optical transmittance at 500 nm for different Cu contents and power sources. Table 1. Properties of Cu/PPFC nanocomposite thin ﬁlms using Cu/PTFE composite targets. b*—yellow Table 1 index. . Properties of Cu/PPFC nanocomposite thin films using Cu/PTFE composite targets. b*—yellow index. Contact Angle Sheet Resistance Transmittance Target Power Type b* (deg.) (W/sq) (%) Power Contact Angle Sheet Resistance Transmittance Target b* Pure PTFE RF 109.83 0.42 over 90.56 0.27 0.69 0.06 Type (deg.) (Ω/sq) (%) Cu Pure 20/PTFE PTFE 80 RF RF 109 100.34 .83 ± 0.4 0.33 2 ov over er 9 89.92 0.56 ± 0 0.29 .27 1.31 0.69 ± 0.04 0.06 Cu 20/PTFE 80 RF 100.34 ± 0.33 over 89.92 ± 0.29 1.31 ± 0.04 Cu 50/PTFE 50 RF 95.85 0.44 over 89.49 0.32 1.37 0.04 Cu 50/PTFE 50 RF 95.85 ± 0.44 over 89.49 ± 0.32 1.37 ± 0.04 Cu 80/PTFE 20 RF 76.67 0.19 over 64.80 0.33 14.30 0.08 Cu 80/PTFE 20 RF 76.67 ± 0.19 over 4 64.80 ± 0.33 14.30 ± 0.08 Cu 80/PTFE 20 MF 12.10 0.48 2.00 0.21 (10 ) 15.68 0.21 22.39 0.15 Cu 80/PTFE 20 MF 12.10 ± 0.48 2.00 ± 0.21 (×10 ) 15.68 ± 0.21 22.39 ± 0.15 Cu 80/PTFE 20 DC 48.31 0.33 34.55 1.40 5.62 0.11 6.48 0.05 Cu 80/PTFE 20 DC 48.31 ± 0.33 34.55 ± 1.40 5.62 ± 0.11 6.48 ± 0.05 Figure 5a shows the XRD patterns of the Cu/PPFC nanocomposite thin ﬁlms prepared by RF Figure 5a shows the XRD patterns of the Cu/PPFC nanocomposite thin films prepared by RF sputtering. The XRD pattern of the PTFE RF thin ﬁlm shows a broad peak around 2 = 23 , implying sputtering. The XRD pattern of the PTFE RF thin film shows a broad peak around 2θ = 23°, implying that the thin ﬁlm is amorphous. Cu 20 RF also exhibited an amorphous state, indicating that the Cu that the thin film is amorphous. Cu 20 RF also exhibited an amorphous state, indicating that the Cu content is randomly distributed in the polymer matrix without forming clusters. The XRD patterns of content is randomly distributed in the polymer matrix without forming clusters. The XRD patterns the Cu 50 RF thin ﬁlms showed Bragg peaks attributed to the (200) crystal face of Cu at 2 50.6 . of the Cu 50 RF thin films showed Bragg peaks attributed to the (200) crystal face of Cu at 2θ ≈ 50.6°. These results are clear evidence that the Cu/PPFC nanocomposite is well formed. The Cu 80 RF These results are clear evidence that the Cu/PPFC nanocomposite is well formed. The Cu 80 RF thin thin ﬁlms showed Bragg peaks due to CuF and Cu O crystals. Considering that the Cu/PPFC 2 2 films showed Bragg peaks due to CuF2 and Cu2O crystals. Considering that the Cu/PPFC nanocomposite thin ﬁlm was fabricated in an argon atmosphere under vacuum, it is considered nanocomposite thin film was fabricated in an argon atmosphere under vacuum, it is considered that that the Cu O crystal peaks were due to the oxidation of Cu when the thin ﬁlm was exposed to air. the Cu2O crystal peaks were due to the oxidation of Cu when the thin film was exposed to air. Unexpectedly, Cu crystalline peaks were not observed in the Cu 80 RF thin ﬁlm. Figure 5b shows the Unexpectedly, Cu crystalline peaks were not observed in the Cu 80 RF thin film. Figure 5b shows the XRD patterns of the Cu 80 RF, MF, and DC nanocomposite thin ﬁlms. Unlike the Cu 80 RF thin ﬁlms, XRD patterns of the Cu 80 RF, MF, and DC nanocomposite thin films. Unlike the Cu 80 RF thin films, which only exhibit CuF and Cu O crystal phases, the XRD patterns of the Cu/PPFC nanocomposite 2 2 which only exhibit CuF2 and Cu2O crystal phases, the XRD patterns of the Cu/PPFC nanocomposite thin ﬁlms prepared by DC and MF sputtering show a Cu cubic crystal phase at 2 40.5 , Cu O cubic thin films prepared by DC and MF sputtering show a Cu cubic crystal phase at 2θ ≈ 40.5°, Cu 2O crystal phase at 2 36.6 , and CuCO monoclinic crystal phase at 2 25.8 [32,33]. The fraction cubic crystal phase at 2θ ≈ 36.6°, and CuCO3 monoclinic crystal phase at 2θ ≈ 25.8° [32,33]. The of the Cu crystal phase calculated from the XRD patterns of the Cu 80 MF and Cu 80 DC thin ﬁlms fraction of the Cu crystal phase calculated from the XRD patterns of the Cu 80 MF and Cu 80 DC thin was 14.2% and 21.1%, respectively, whereas that in the Cu 80 DC thin ﬁlms showed larger values. films was 14.2% and 21.1%, respectively, whereas that in the Cu 80 DC thin films showed larger The crystal size of the Cu 80 MF and Cu 80 DC thin ﬁlms, as calculated by the Debye–Scherrer equation values. The crystal size of the Cu 80 MF and Cu 80 DC thin films, as calculated by the Debye– (D = 0.916/ cos , D: Crystalline size, : X-ray wavelength, : Full width half-maximum (FWHM) of Scherrer equation (D = 0.916λ/βcos θ, D: Crystalline size, λ: X-ray wavelength, β: Full width Bragg peak, : Scattering angle), was about 5 nm [32]. half-maximum (FWHM) of Bragg peak, θ: Scattering angle), was about 5 nm [32]. Appl. Sci. 2019, 9, 1296 7 of 10 Appl. Sci. 2019, 9, x FOR PEER REVIEW 7 of 10 Figure 5. XRD patterns of (a) pure PTFE, Cu 20 RF, Cu 50 RF, Cu 80 RF, and (b) Cu 80 RF, Cu 80 MF, Figure 5. XRD patterns of (a) pure PTFE, Cu 20 RF, Cu 50 RF, Cu 80 RF, and (b) Cu 80 RF, Cu 80 MF, and Cu 80 DC nanocomposite thin ﬁlms. and Cu 80 DC nanocomposite thin films. The chemical structure of the Cu/PPFC nanocomposite thin ﬁlms was analyzed by XPS. The intensity The chemi ofca the l struc binding ture oener f the gy Cu/ was PPFC calibrated nanocom based posite on ththe in fil position ms was of ana the lyzed C–C by bond XPS. (sp The intensity of the binding energy was calibrated based on the position of the C–C bond (sp hybrid hybrid orbital, 284.8 eV). Figure 6a shows the normalized C 1s core-level XPS spectra of the Cu/PPFC nanocomposite orbital, 284.8 eV thin ). Fiﬁlms gure pr 6aepar shoed ws by the RF no sputtering rmalized C of1the s co Cu/PTFE re-level Xcomposite PS spectra tar of get. the The Cu/PP C FC 1s nanocomposite thin films prepared by RF sputtering of the Cu/PTFE composite target. The C 1s spectra exhibit broad Gaussian deconvolution peaks that have the following customary assignments for spec a tra ﬂuor exhi ocarbon bit brothin ad Gﬁlm: aussia 294.0 n dec eV onv (CF oluti ),o 292.0 n peaeV ks t(CF hat ha ), 289.8 ve theeV foll (CF), owin287.5 g custo eV m(C–CF ary assi), gn and ment an s 3 2 n for a fluorocarbon thin film: 294.0 eV (CF3), 292.0 eV (CF2), 289.8 eV (CF), 287.5 eV (C–CFn), and an additional C=O peak at 288.6 eV owing to binding with oxygen [16,31,34]. The intensity of the CF bond, additio which nal C= is O typical peak ain t 28 a8ﬂuor .6 eV ocarbon owing to thin bin ﬁlm, ding is wi decr th o eased xygenowing [16,31,to 34] the . The low inﬂuorine tensity obonding f the CF2 bond, which is typical in a fluorocarbon thin film, is decreased owing to the low fluorine bonding ratio and high carbon bonding ratio in the thin ﬁlm with increasing Cu content. In the Cu 80 RF thin ﬁlm, ratio the and composition high carbonratio bond of inﬂuorine g ratio in was the drastically thin film wi decr th ieased, ncreasi and ng C most u con of tent. the Ibonds n the Cu wer 8e 0 formed RF thin film, the composition ratio of fluorine was drastically decreased, and most of the bonds were formed between carbon and oxygen (C=O) upon exposure of the thin ﬁlm to air. In the Cu 80 RF thin ﬁlm, the betwee bonding n carb ratio on an of d ﬂuorine oxygen (decr C=O) eased uponsharply exposure , and of the the bond thin fibetwe lm to en air.carbon In the Cu and8oxygen 0 RF thin (C=O) film, the bonding ratio of fluorine decreased sharply, and the bond between carbon and oxygen (C=O) appeared after air exposure of the thin ﬁlm. Figure 6b shows that the C 1s core-level spectra of the Cu 80 appe RFa , re Cu d 80 after MF a,ir and expo Cu sur 80 e DC of th thin e thﬁlms in film have . Figure no binding 6b show ener s thgy at th peaks e C 1due s core to-l the evel CF spec bond, tra ofand the Cu 80 RF, Cu 80 MF, and Cu 80 DC thin films have no binding energy peaks due to the CF 2 bond, that the carbon bond is dominant. The Cu 2p spectra of the Cu/PPFC nanocomposite thin ﬁlms are shown and tha in t th Figur e car eb6 oc. n b The ond Cu is 20 dom RF inand ant. Cu The 50 Cu RF 2p thin spec ﬁlms tra oshowed f the Cu/almost PPFC n no ano binding composi ener te th gy in peak, films are shown in Figure 6c. The Cu 20 RF and Cu 50 RF thin films showed almost no binding energy whereas the Cu 80 RF, Cu 80 MF, and Cu 80 DC thin ﬁlms showed Cu 2p binding energy peaks 3/2 at pe932.7 ak, wh eV ere and as th ae Cu Cu2p 80 RF, binding Cu 80 ener MF, gy and peak Cu at 80 952.6 DC th eV in ( fD ilm BE s = sh19.9 owed eV) Cu [12 2p ]. 3/2In bithe ndin Cu g e80 ner RF gy 1/2 peaks at 932.7 eV and a Cu 2p1/2 binding energy peak at 952.6 eV (ΔBE = 19.9 eV) [12]. In the Cu 80 RF thin ﬁlm, CuCO binding energy peaks were observed at 934.6 eV (Cu 2p ) and 954.5 eV (Cu 2p ), 3 3/2 3/2 which thin filis mpr , CuC esumably O3 bind due ing to en surfac ergy pe e oxidation aks were o after bserthin ved a ﬁlm t 93fabrication. 4.6 eV (Cu 2A p3/2 shake-up ) and 954satellite .5 eV (Cu peak 2p3/2 of ), 2+ 9 which is presumably due to surface oxidation after thin film fabrication. A shake-up satellite peak of Cu [Ar] 3d orbital conﬁguration was observed in the binding energy range of 938.5–946.0 eV (Cu 2+ 9 2p Cu ) [A and r] 3959.0–965 d orbital co eV nf(Cu igura 2p tion ). wShake-up as observed satellite in the peaks bindin appear g energy str r ongly ange o when f 938.Cu 5–94 is 6.oxidized 0 eV (Cu 3/2 1/2 2p3/2) and 959.0–965 eV (Cu 2p1/2). Shake-up satellite peaks appear strongly when Cu is oxidized to to form CuO or CuF . Thus, the Cu 80 DC thin ﬁlm exhibits excellent conductivity, a large crystal form CuO or CuF2. Thus, the Cu 80 DC thin film exhibits excellent conductivity, a large crystal size size of Cu, as well as a low oxidation degree. Figure 6d shows the chemical quantiﬁcation results, of Cu, as well as a low oxidation degree. Figure 6d shows the chemical quantification results, obtained by considering the relative sensitivity factors of each binding energy peak in the XPS spectra. obtained by considering the relative sensitivity factors of each binding energy peak in the XPS As the weight ratio of Cu increases from Cu 20 wt.% (9.12 mol%) to 50 wt.% (20.8 mol%) and 80 spectra. As the weight ratio of Cu increases from Cu 20 wt.% (9.12 mol%) to 50 wt.% (20.8 mol%) wt.% (51.2 mol%) in the Cu/PTFE composite target, the dramatic change in the physical properties and 80 wt.% (51.2 mol%) in the Cu/PTFE composite target, the dramatic change in the physical of the Cu/PPFC nanocomposite thin ﬁlm is attributed to the difference in the quantitative ratio of properties of the Cu/PPFC nanocomposite thin film is attributed to the difference in the quantitative copper atoms and ﬂuorine atoms in the Cu/PPFC nanocomposite thin ﬁlm. Cu concentration of the ratio of copper atoms and fluorine atoms in the Cu/PPFC nanocomposite thin film. Cu concentration nanocomposite thin ﬁlms Cu 20 RF (0.10%), Cu 50 RF (0.27%), and Cu 80 RF (6.51%) were different of the nanocomposite thin films Cu 20 RF (0.10%), Cu 50 RF (0.27%), and Cu 80 RF (6.51%) were from the composite targets but also gradually increased. different from the composite targets but also gradually increased. Appl. Sci. 2019, 9, 1296 8 of 10 Appl. Sci. 2019, 9, x FOR PEER REVIEW 8 of 10 Figure 6. Normalized XPS spectra of (a) C 1s with increasing Cu content, (b) C 1s with RF, MF, and DC Figure 6. Normalized XPS spectra of (a) C 1s with increasing Cu content, (b) C 1s with RF, MF, and power sources, and (c) Cu 2p for the Cu/PPFC nanocomposite thin ﬁlms with varying Cu contents DC power sources, and (c) Cu 2p for the Cu/PPFC nanocomposite thin films with varying Cu and power sources. (d) Calculated carbon, ﬂuorine, and copper ratio for the nanocomposite Cu/PPFC contents and power sources. (d) Calculated carbon, fluorine, and copper ratio for the nanocomposite nanocomposite thin ﬁlms. Cu/PPFC nanocomposite thin films. 4. Conclusions 4. Conclusions In summary, we have successfully fabricated Cu/PTFE composite targets with various Cu weight In summary, we have successfully fabricated Cu/PTFE composite targets with various Cu percentages for sputtering and deposited Cu/PPFC nanocomposite thin ﬁlms. This was followed by weight percentages for sputtering and deposited Cu/PPFC nanocomposite thin films. This was analysis of the properties of the Cu/PPFC nanocomposite thin ﬁlms with respect to the Cu composition followed by analysis of the properties of the Cu/PPFC nanocomposite thin films with respect to the ratio. The Cu nanoclusters were well distributed in a spherical shape with a size of 10–20 nm examined Cu composition ratio. The Cu nanoclusters were well distributed in a spherical shape with a size of by a FE-TEM image. The Cu/PPFC nanocomposite ﬁlms prepared by RF sputtering with Cu 20 and 50 10–20 nm examined by a FE-TEM image. The Cu/PPFC nanocomposite films prepared by RF targets showed very similar transmittance and color characteristics to those of pure PTFE. However, sputtering with Cu 20 and 50 targets showed very similar transmittance and color characteristics to the water contact angle gradually decreased owing to the Cu on the ﬁlm surface. The effect of Cu those of pure PTFE. However, the water contact angle gradually decreased owing to the Cu on the content was more pronounced in the Cu 80 target. The Cu 80 target has excellent conductivity and can film surface. The effect of Cu content was more pronounced in the Cu 80 target. The Cu 80 target has be sputtered not only in RF but also in MF and DC power sources; moreover, the physical properties excellent conductivity and can be sputtered not only in RF but also in MF and DC power sources; of the thin ﬁlm change signiﬁcantly depending on the power source. Interestingly, the Cu 80 MF moreover, the physical properties of the thin film change significantly depending on the power and Cu 80 DC thin ﬁlms exhibited absorption peaks at 618 and 678 nm, respectively, indicating that source. Interestingly, the Cu 80 MF and Cu 80 DC thin films exhibited absorption peaks at 618 and the Cu nanoclusters were well formed. Further, from the red shift of the absorption peak, it can be 678 nm, respectively, indicating that the Cu nanoclusters were well formed. Further, from the red assumed that the size of the nanoclusters prepared using DC was larger than that using MF, which is shift of the absorption peak, it can be assumed that the size of the nanoclusters prepared using DC also why the nanocomposite ﬁlms prepared by MF and DC exhibit sheet resistances of 2 10 and was larger than that using MF, which is also why the nanocomposite films prepared by MF and DC 34.55 W/sq, respectively, thus explaining why the electrical properties of the thin ﬁlms prepared using exhibit sheet resistances of 2 × 10 and 34.55 Ω/sq, respectively, thus explaining why the electrical DC are superior. properties of the thin films prepared using DC are superior. This study describes a novel method to fabricate metal–polymer nanocomposites. This method This study describes a novel method to fabricate metal–polymer nanocomposites. This method can be expanded and diversiﬁed to easily fabricate not only various metal nanocomposites but also can be expanded and diversified to easily fabricate not only various metal nanocomposites but also ceramics and semiconductor nanocomposites. Therefore, this method is industrially promising, as it enables fabrication over a large area and in a continuous manner. Appl. Sci. 2019, 9, 1296 9 of 10 ceramics and semiconductor nanocomposites. Therefore, this method is industrially promising, as it enables fabrication over a large area and in a continuous manner. Author Contributions: S.-J.L. designed the study and the experiments. S.H.K. fabricated the Cu/PPFC thin ﬁlms using a test sputter system. S.H.K., M.K., and J.S.P. analyzed the properties of the Cu/PPFC thin ﬁlms. S.-J.L. and M.K. wrote the manuscript. All of the authors discussed the results and commented on the manuscript. 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Optical, Electrical, and Surface Properties of Cu/Plasma Polymer Fluorocarbon Nanocomposite Thin Film Fabricated Using Metal/Polymer Composite Target

Optical, Electrical, and Surface Properties of Cu/Plasma Polymer Fluorocarbon Nanocomposite Thin Film Fabricated Using Metal/Polymer Composite Target

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Optical, Electrical, and Surface Properties of Cu/Plasma Polymer Fluorocarbon Nanocomposite Thin Film Fabricated Using Metal/Polymer Composite Target

Optical, Electrical, and Surface Properties of Cu/Plasma Polymer Fluorocarbon Nanocomposite Thin Film Fabricated Using Metal/Polymer Composite Target

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