Effects of process parameters on optical characteristics of diamond-like carbon thin films deposited using high-power impulse magnetron sputtering

Journal Pre-proof Effects of process parameters on optical characteristics of diamond-like carbon thin films deposited using high-power impulse magnetron sputtering

Jian-Fu Tang, Yi-Jing Tsai, Chun-Hong Huang, Ching-Yen Lin, Fu-Chi Yang, Jenn-Jiang Hwang, Chi-Lung Chang PII:

S0040-6090(19)30590-5

DOI:

https://doi.org/10.1016/j.tsf.2019.137562

Reference:

TSF 137562

To appear in:

Thin Solid Films

Received date:

13 February 2019

Revised date:

5 August 2019

Accepted date:

10 September 2019

Please cite this article as: J.-F. Tang, Y.-J. Tsai, C.-H. Huang, et al., Effects of process parameters on optical characteristics of diamond-like carbon thin films deposited using high-power impulse magnetron sputtering, Thin Solid Films (2019), https://doi.org/ 10.1016/j.tsf.2019.137562

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© 2019 Published by Elsevier.

Journal Pre-proof Effects of process parameters on optical characteristics of diamond-like carbon thin films deposited using high-power impulse magnetron sputtering

Jian-Fu Tanga, Yi-Jing Tsaib, Chun-Hong Huangb, Ching-Yen Linb, Fu-Chi Yangc, Jenn-Jiang

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Hwanga, Chi-Lung Changb, c, *

Department of Greenergy Technology, National University of Tainan, Taiwan

b

Department of Materials Engineering, Ming Chi University of Technology, Taiwan

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Center for Plasma and Thin Film Technologies, Ming Chi University of Technology, Taiwan

*

Corresponding author: Chi-Lung Chang

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E-mail address: [email protected] TEL: +886-2-29089899

FAX: +886-2-29084091

Journal Pre-proof Abstract High-power impulse magnetron sputtering (HiPIMS) is a physical vapor deposition technique, developed specifically for the low-temperature deposition of functional thin films. In this study, a graphite target was used for the deposition of diamond-like carbon (DLC) thin films of high optical transmittance on a quartz glass substrate at 25°C – 30°C using HiPIMS in unipolar and bipolar modes.

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Experiments were conducted to determine the influence of DC input power, deposition time, and bias voltage with a fixed duty cycle on the optical characteristics of the resulting amorphous DLC thin

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films. During deposition, the current-voltage characteristics of discharge with a graphite target were

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recorded. The optical characteristics were assessed using a UV/visible light-absorption detector and the structure of the DLC thin films was confirmed by Raman spectroscopy. DLC thin films produced

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in unipolar mode with deposition time of 1 minute presented the highest best transmittance of 86%.

Keywords: Diamond like carbon; High-power impulse magnetron sputtering; Optical transmittance; Graphite

Journal Pre-proof 1.

Introduction

Ultra-thin transparent diamond-like carbon (DLC) films could be widely used to replace sapphire materials as optical glass; however, the preparation of the glass substrate and deposition process must first be optimized [1] [2]. DLC thin films can be divided into hydrogenated (a-C:H) and nonhydrogenated (a-C) [3]. When prepared under suitable synthesis conditions, hydrogenated DLC films

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such as ta-C:H are transparent in the visible light range. The a-C:H films have been also developed under a variety of gas conditions in order to tailor their properties to specific applications. Suzuki et al.

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[4] reported that a film deposited from a mixture gas of CH4+H2 s presented particularly high optical

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transmittance (~85 %). Currently, the applicability of a-C thin films in optical devices is limited by high reflectivity, and the lack of transparency limits the thickness to which they can be applied. Thus

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films.

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far, researchers have dedicated relatively little effort to modifying the optical properties of a-C thin

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DLC films are made up almost entirely of carbon bonds (sp3 and sp2); and their characteristics vary greatly with processing conditions. Sp3 carbon bonds mainly affect the mechanical properties of the resulting film, whereas sp2 bonds tend to affect the electrical and optical properties [5]. Thus, the ratio of sp2 and sp3 bonds largely determines the overall properties of DLC films. Numerous methods have been developed for the deposition of DLC thin films. The most common approaches include cathodic arc evaporation [6] [7], chemical vapor deposition [8, 9], pulsed laser deposition [10], and magnetron sputtering [11]. The average transmittance of the DLC coating prepared by Chan et al. [12] using dc-remote plasma enhancement chemical vapor deposition was

Journal Pre-proof approximately 82% in the full-wave domain. Su et al. [13] reported that decreasing the thickness by limiting the deposition time and/or increasing the cavity pressure in an unbalanced magnetron sputtering system could produce DLC thin films with improved transmittance of visible light. Under optimal parameters, the transmittance of films in the visible region can reach 85%. The objective in this study was to improve the optical properties of DLC thin films by adjusting the

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process parameters of high-power impulse magnetron sputtering (HiPIMS), which is a recent breakthrough in coating technology. Unlike conventional physical vapor deposition methods,

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HiPIMS features a large ionization fraction of the target species under low deposition temperatures

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[14, 15].

HiPIMS discharge current can reach hundreds of amperes and plasma power can reach several

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megawatts within just a few hundred microseconds (ms) [16], which makes HiPIMS technology

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superior to conventional magnetron sputtering in terms of bombardment energy. This has proven

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highly beneficial to the density, surface roughness, and adhesion of the resulting DLC thin films. It has also been shown to reduce arc poisoning of the target and eliminate instability in the transition region. There has been relatively little research on the use of HiPIMS to fabricate transparent DLC films, and most of that work has focused on process parameters, such as deposition time, power, and pressure. [17] [18] In most applications, operators select a single operating mode (unipolar or bipolar), depending on the configuration of the apparatus and/or the characteristics of the application target. Note that bipolar mode is seldom used for thin film deposition. Tiron et al. reported that bipolar mode with added bias

Journal Pre-proof voltage produces copper thin films possessing a structure superior to those obtained in unipolar mode [19]. In the current study, all experiments on processing parameters were conducted in both operating modes and the resulting DLC thin films were compared in terms of optical quality.

2. Experiment details

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The DLC films were deposited on quartz glass substrates by sputtering a rectangular graphite target (532 mm ×214.5 mm × 10 mm) under Ar gas in a chamber measuring Φ 900 mm × 1000 mm (LightJet

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UHV Co., LTD., Hsinchu, Taiwan). The purity of the graphite target in this study was 99.99 at.%.

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Throughout the deposition process, the temperature was controlled to between 25 °C ~ 30 °C. The parameters are detailed in Table 1. The thickness of the DLC thin films was measured via depth

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profiling using Time-of-Flight Secondary Ion Mass Spectrometer (TOF-SIMS, Ion-ToF, Münster,

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Germany) with a 1 keV Cs+ sputter beam and a 30 keV Bi3+ cluster analysis beam. A

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260×260 μm2 area of the sample was sputtered, and the central 100×100 μm2 area was analyzed. The quality of the DLC films grown on the quartz glass substrate was examined using Raman spectroscopy (HORIBA IHR550, AST Instruments Corporation, Japan) with excitation light of 532nm. Our objective in parameter optimization was to produce ultra-thin DLC films with high optical transmittance. The DLC films deposited on the surface of quartz glass under different parameters were assessed using a spectrophotometer (V-670 Jasco Inc, Japan), in transmittance and reflectivity mode at 5 nm intervals in the UV/VIS/NIR regions (190 nm–770 nm) and 8 nm intervals in the NIR region (770 nm–2500 nm). The hardness and elastic modulus of the DLC films were

Journal Pre-proof examined using a nanoindenter (Hysitron TI-900 TriboIndenter, Bruker, Billerica, MA, USA) equipped with a Berkovich 142.3° diamond probe tip. The maximum indentation depth was controlled to within 1/10 of the film thickness to avoid substrate effects, and the loading rate was set at 1000 μN/s. Five indentation tests were performed on each film sample. The primary objective in this study was to produce ultrathin DLC thin films with high optical transmittance through the careful

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adjustment of process parameters. The research process was divided into five stages : 1) analyzing the current-voltage (I-V) characteristics of the instrument and materials, 2) adjusting DC input power,

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3) adjusting deposition time, 4) evaluating the two HiPIMS operating modes, and 5) examining the

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influence of bias voltage.

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3. Results and discussion

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3.1 I–V limit tests for the characterization of graphite target

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HiPIMS technique is usually implemented using a low duty cycle (1–5 %) with low repetition frequency (< 1k Hz), a relatively short pulse on-time (from several μs to thousands of μs), and a longer pulse off-time [20]. In this stage of the experiment, the objective was to determine the frequency and duty cycle, and ensure that the required peak power density of several kW/cm2 was met. Fig. 1 presents measurements of peak power density in HiPIMS pulses of various frequency, duty cycle, and DC input power in unipolar and bipolar modes. The figure shows a distinct increase in peak power density with an increase in DC input power. Similarly, when the duty cycle was decreased, the peak power density increased, and vice versa. The peak power density under low duty

Journal Pre-proof cycle is not presented in all of the figures because the current or voltage exceeded the capacity of the instrument under those parameter settings. Under all parameter settings, there was a smooth increase in peak power density up to the highest values at frequencies of 75 Hz to 150 Hz. At frequencies above this range, the peak power density leveled off. Based on the results in Fig. 1 (b), it was determined that the most suitable duty cycle would be 2.5 % with an optimal frequency of 150 Hz

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3.2 Effects of input power on process parameters

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under unipolar or bipolar operating modes.

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One of the objectives in this study was to elucidate the mechanical properties of DLC produced under various DC input power levels. Considering that most of these films are meant to be used as protective

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surfaces, it is crucial that they meet specified hardness and toughness thresholds. Thus,

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nanoindentation tests were given the highest priority over the other mechanical characteristics.

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Table 2 presents the hardness, Young’s modulus, and H3/E*2 ratios of DLC thin films produced using various DC input powers. When the DC input power was increased from 1500 W to 2500 W, the thickness of thin films increased from 258 nm to 362 nm, the optical transmittance decreased from 66% to 53%, and the hardness and Young’s modulus respectively increased to their maximum levels of 8.5 GPa and 77 GPa. Previous studies reported a decrease in the hardness and Young's modulus concurrent with improvements in the optical transmittance. Suzuki et al. [4] report decreases in hardness (from 17.4 to 4.3 GPa) and Young's modulus (from 175 to 34 GPa) as the optical transmittance increased (from 69% to 98%). Kim et al. [21] reported on a a-C:H film deposited at

Journal Pre-proof 150 W with maximum hardness of 5.4 GPa and transmittance exceeding 60%. The increase in hardness can be attributed to the fact that a higher DC input power tends to improve the crystallinity of thin films by enhancing the intensity of ion bombardment [22]. Hecimovic et al. [23] reported that increasing the peak current and voltage led to a steady increase in the relative number of high energy ions under low pressure conditions. Lin et al. [24] reported increasing the peak

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power promoted the ionization of the target and gas species in HiPIMS plasma. They also reported changes in ion energy when the DC input power was increased. Robertson et al. [25] observed that

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the hardness and diamond-like characteristics of a-C depend heavily on ion energy.

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The highest H3/E*2 ratio was obtained under a DC input power of 2500 W. Based on these results, we opted for a fixed output power of 2.5 kW, under which subsequent parameter setting would be

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adjusted.

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3.3 Effects of deposition time on process parameters Fig. 2 presents (a) the transmittance curves and (b) a graph indicating the trend in reflectivity of DLC thin films produced using various deposition times. Transmittance in the UV, visible light, and NIR regions increased sharply with deposition time up to 15 minutes. Increasing the deposition time beyond 15 minutes resulted in DLC thin films that were unsuitable as optical thin films, due to the low transmittance of visible light, which was far lower than that of glass (visible light: 90 %). The film produced using a deposition time of 1 minute presented the highest transmittance of 82 % (UV: 38 %, visible light: 71 %, NIR: 87 %). As shown in Fig. 2 (b), the film produced using a

Journal Pre-proof deposition time of 1 minute also presented the lowest reflectance of 10 % with NIR reflectance of 8 %, which is close to that of the underlying glass. Table 3 details the experiment data pertaining to various optical characteristics. The best optical thin films in this study increased reflectance in the UV region as well as transmittance in the visible light region. Based on these results, we opted for a

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fixed deposition time of 1 minute, under which subsequent parameter setting would be adjusted.

3.4 Effects of HiPIMS operating mode on process parameters

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The Raman spectra of the prepared films were fitted using Gaussian peaks that varied in terms of

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peak width, position, and area. Single crystal graphite has a single Raman active mode, which is the

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zone-centre mode at 1580 cm-1 of E2g symmetry labelled "G" for graphite. Disordered graphite has a

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second mode at around 1350 cm-1 of A1g symmetry labelled "D" for disorder [26]. Fig. 3 presents the

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Raman spectra of DLC (a-C) films prepared on a silicon substrate using various deposition times.

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Under excitation of λ=514.5 nm, the spectra present a broad Raman band between 1000 and 1800 cm-1. It was fitted using two Gaussian curves on a linear background, centered at 1300...1380 cm-1 and 1520...1580 cm-1, respectively [27]. As shown in Fig. 3, the flat band that appeared below 1000 cm-1 corresponds to the silicon substrate [28]. Table 4 lists the Raman spectra and ID/IG data. Fig. 4 presents the transmittance and reflectivity curves of DLC thin film fabricated under the two HiPIMS modes. The thickness of DLC films produced using deposition times of 1 and 5 minutes were 30 nm and 80 nm, respectively. The average transmittance of samples produced in unipolar mode was higher than that of samples produced in bipolar mode, regardless of deposition time (as shown in Fig. 4 (a)).

Journal Pre-proof There was a slight decrease in optical transmittance with an increase in deposition time, due to an increase in film thickness. Breskin et al. [29] reported that the transmittance of DLC thin film could be controlled by varying the ID/IG ratio in the DLC thin film structures. Lin et al. [30] reported that the DLC films with the highest transmittance were those with the highest ID/IG ratio. Table 4 lists the ID/IG ratios of the various films as follows: unipolar, 1 min (0.64), bipolar, 1 min (0.67), unipolar, 5

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min (0.84), and bipolar, 5 min (0.87). Lin et al. [17] reported that higher peak target current densities reduced the ID/IG ratio and increased film density. As shown in Fig. 1(a) (c), the peak power density

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obtained in unipolar mode was higher than that obtained in bipolar mode (under same DC input power

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conditions), such that the resulting DLC thin film presented higher transmittance, due to its I D/IG ratio associated with a higher peak power density.

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These results demonstrate that unipolar operating mode is superior to bipolar operating mode in terms

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of transmittance performance. The film produced in unipolar mode with deposition time of 1 minute

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achieved visible light transmittance of 75 %. Operating mode did not appear to have any effect of reflectance in the UV, visible light, or NIR regions (Fig. 4(b)). The reflectance of DLC thin films depends entirely on thickness. Based on these results, we opted to use unipolar mode in all subsequent experiments.

3.5 Effects of bias voltage on process parameters Fig. 5 presents (a) transmittance and (b) reflectivity curves of DLC thin films fabricated under various bias voltage settings. Zhang et al. [31] reported that the ID/IG ratio of the DLC films could be increased

Journal Pre-proof dramatically simply by increasing the bias voltage. In this study, increasing the bias voltage to -180 V led to a slight decrease in optical transmittance, and this effect was most pronounced at visible wavelengths. Regardless of whether bias voltage was added, the average transmittance at NIR wavelengths exceeded 88%, which is very close to that of glass (90 %). As shown in Fig. 5 (b), the reflectance of the DLC thin films in the NIR region was unaffected by changes in bias voltage. Overall,

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the average reflectance (10 %) of the DLC thin films was very close to that of glass (8 %). The absorption coefficient α is defined as the fractional decrease in intensity per unit increase in distance.

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It is knows from Beer–Lambert's law that the absorption coefficient α is given by: α = (1/d)[log(1/T)],

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where d is the path length that the light travels in cm and T is the transmittance recorded from the

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samples. Fig. 6 plots the absorption coefficient α vs. energy hν of DLC thin films deposited under

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various bias voltage settings. In the two other types of film, α increased with an increase in the energy

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values. The absorption coefficients of the a-C films on glass increased with an increase in bias voltage.

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Thus, it appears that bipolar mode with added bias voltage is superior to unipolar mode.

4. Conclusions In this work, we investigated the effects of various process parameters on the optical characteristics of DLC thin films deposited using HiPIMS. These results indicate that the hardness and thickness of DLC thin films increased with an increase in DC input power. However, average transmittance in the full wave domain decreased with an increase in DC input power. Average transmittance (%) decreased with an increase in coating thickness (or deposition time). The average transmittance (%) of thin films

Journal Pre-proof fabricated in HiPIMS unipolar mode were higher than that of films fabricated in bipolar mode. The DLC film fabricated under a deposition time of one minute presented the highest UV reflectance. The DLC film with the highest transmittance (86%) was obtained in unipolar mode with deposition time of 1 minute without added bias voltage.

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Acknowledgments The authors would like to thank the Ministry of Science and Technology, Taiwan, R.O.C for

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financially supporting this research project under grant No. MOST 107-2622-E-131-001-CC2,

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MOST 106-2218-E-131-003, and MOST 107-2221-E-131-003.

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[6] P.-C. Tsai, K.-H. Chen, Evaluation of microstructures and mechanical properties of diamond like carbon films deposited by filtered cathodic arc plasma, Thin Solid Films, 516 (2008) 5440-5444.

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[7] C.-L. Chang, J.-Y. Jao, T.-C. Chang, W.-Y. Ho, D.-Y. Wang, Influences of bias voltage on properties of TiAl-doped DLC coatings synthesized by cathodic arc evaporation, Diamond Relat. Mater., 14 (2005) 2127-2132.

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[8] Y. Kim, S. Cho, W. Choi, B. Hong, D. Yoon, Dependence of the bonding structure of DLC thin films on the deposition conditions of PECVD method, Surf. Coat. Technol., 169 (2003) 291-294.

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[9] S. Sainio, T. Palomäki, S. Rhode, M. Kauppila, O. Pitkänen, T. Selkälä, G. Toth, M. Moram, K. Kordas, J. Koskinen, Carbon nanotube (CNT) forest grown on diamond-like carbon (DLC) thin films significantly improves electrochemical sensitivity and selectivity towards dopamine, Sensors Actuators B: Chem., 211 (2015) 177-186.

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[10] W. Kautek, S. Pentzien, A. Conradi, J. Krüger, K.-W. Brzezinka, Pulsed-laser deposition and boron-blending of

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diamond-like carbon (DLC) thin films, Appl. Surf. Sci., 106 (1996) 158-165. [11] S. Khamseh, E. Alibakhshi, M. Mahdavian, M.R. Saeb, H. Vahabi, N. Kokanyan, P. Laheurte, Magnetron-sputtered

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copper/diamond-like carbon composite thin films with super anti-corrosion properties, Surf. Coat. Technol., 333

[12] M.-S. Hwang, E.-T. Kim, C. Lee, Effects of DC power on the properties of DLC coatings on the OPC drum, J. Electron. Mater., 30 (2001) 78-83.

[13] C.H. Su, C.R. Lin, C.Y. Chang, H.C. Hung, T.Y. Lin, Mechanical and optical properties of diamond-like carbon thin films deposited by low temperature process, Thin Solid Films, 498 (2006) 220-223. [14] K. Sarakinos, J. Alami, S. Konstantinidis, High power pulsed magnetron sputtering: A review on scientific and engineering state of the art, Surf. Coat. Technol., 204 (2011) 1661-1684. [15] J.C. Oliveira, F. Ferreira, A. Anders, A. Cavaleiro, Reduced atomic shadowing in HiPIMS: Role of the thermalized metal ions, Appl. Surf. Sci., 433 (2018) 934-944. [16] A. Anders, A review comparing cathodic arcs and high power impulse magnetron sputtering (HiPIMS), Surf. Coat. Technol., 257 (2014) 308-325. [17] J. Lin, W.D. Sproul, R. Wei, R. Chistyakov, Diamond like carbon films deposited by HiPIMS using oscillatory voltage pulses, Surf. Coat. Technol., 258 (2014) 1212-1222. [18] T. Konishi, K. Yukimura, K. Takaki, Fabrication of diamond-like carbon films using short-pulse HiPIMS, Surf. Coat. Technol., 286 (2016) 239-245.

Journal Pre-proof [19] I.-L. Velicu, G.-T. Ianoş, C. Porosnicu, I. Mihăilă, I. Burducea, A. Velea, D. Cristea, D. Munteanu, V. Tiron, Energyenhanced deposition of copper thin films by bipolar high power impulse magnetron sputtering, Surf. Coat. Technol., 359 (2018) 97-107. [20] C.-L. Chang, F.-C. Yang, Synthesis and characteristics of nc-WC/aC: H thin films deposited via a reactive HIPIMS process using optical emission spectrometry feedback control, Surf. Coat. Technol., 350 (2018)1120-1127. [21] J.-D. Kim, H. Sugimura, O. Takai, Water-repellency of aC: H films deposited by rf plasma-enhanced CVD, Vacuum, 66 (2002) 379-383. [22] H.T. Kim, C.S. Chae, D.H. Han, D.K. Park, Effect of substrate temperature and input power on TiN film deposition by low-frequency (60 Hz) PECVD, JOURNAL-KOREAN PHYSICAL SOCIETY, 37 (2000) 319-323. [23] A. Hecimovic, K. Burcalova, A. Ehiasarian, Origins of ion energy distribution function (IEDF) in high power impulse magnetron sputtering (HIPIMS) plasma discharge, J. Phys. D: Appl. Phys., 41 (2008) 095203.

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[24] J. Lin, J.J. Moore, W.D. Sproul, B. Mishra, Z. Wu, Modulated pulse power sputtered chromium coatings, Thin Solid

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Films, 518 (2009) 1566-1570.

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[26] J. Robertson, Diamond-like amorphous carbon, Materials science and engineering: R: Reports, 37 (2002) 129-281. [27] G. Irmer, A. Dorner‐Reisel, Micro‐Raman studies on DLC coatings, Adv. Eng. Mater., 7 (2005) 694-705.

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[28] N. Menegazzo, M. Kahn, R. Berghauser, W. Waldhauser, B. Mizaikoff, Nitrogen-doped diamond-like carbon as optically transparent electrode for infrared attenuated total reflection spectroelectrochemistry, Analyst, 136 (2011)

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composition, Diamond Relat. Mater., 6 (1997) 687-693.

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[30] C. Lin, D. Wei, C. Chang, W. Liao, Optical properties of diamond-like carbon films for antireflection coating by RF magnetron sputtering method, Physics Procedia, 18 (2011) 46-50.

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[31] W. Zhang, A. Tanaka, K. Wazumi, Y. Koga, Structural, mechanical and tribological properties of diamond-like carbon films prepared under different substrate bias voltage, Diamond Relat. Mater., 11 (2002) 1837-1844.

Journal Pre-proof Figure Captions :

Fig. 1 Peak power density of HiPIMS pulses of various frequency, duty cycle, and DC input power: (a) (b) unipolar mode and (c) (d) bipolar mode. Fig. 2 (a) Transmittance curves and (b) graph illustrating trend in reflectivity values of DLC thin films produced using various deposition times.

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Fig. 3 Raman spectra of DLC films produced using various deposition times. Fig. 4 Transmittance and reflectivity curves of DLC thin film using the two HiPIMS modes.

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Fig. 5 (a) Transmittance and (b) reflectivity curves of DLC thin film obtained under various bias

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voltage settings.

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Fig. 6 Absorption coefficient, α, as a function of photo energy, hν in DLC films deposited under

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various bias voltage settings.

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Highlights Two operating modes for HiPIMS were used: Bipolar and Unipolar..

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Non-hydrogenated DLC films are transparent in visible light range.

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The best transmittance of 86% for the DLC can be obtained in unipolar mode.

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UV reflection of DLC film is increased to 20%.

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Journal Pre-proof Table 1: Experiment parameters of the DLC thin films deposited by HiPIMS Values

Carbon materials (99.99 at.%)

C

Target-substrate distance (cm)

15

Operating pressure (Pa)

0.44

Input power (kW)

1.5, 2, 2.5

Working gas

Ar

Depositing time of DLC film (min)

1, 5, 10, 15, 20, 25, 30, 35

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Parameter

Duty cycle (%)

2.5

0, 60, 180

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Dc bias voltage (V)

150

Pulse on-time/off-time (μs)

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Operating mode

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Pulse frequency (Hz)

166/6489 Bipolar, Unipolar

Journal Pre-proof Table 2: Hardness, Young’s modulus, and H3/E*2 ratio of DLC thin films deposited by HiPIMS at various DC input power levels DC input power (W)

Young’s modulus

Hardness (GPa)

H3/E*2 ratios

(GPa)

6.3

58

0.076

2000

7.3

70

0.083

2500

8.5

77

0.105

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Pr

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1500

Journal Pre-proof Table 3: The experimental data of a various characteristics of DLC thin films deposited by HiPIMS

Mode

Input

Depositi

power

on time

(kW)

(min)

Glass

Average Transmittance (%) Bias

Thickness

(-V)

(nm)

Average Reflectance (%)

Full wave

UV

Visible

NIR

Full wave

UV

Visible

NIR

domain

light

light

light

domain

light

light

light

-

89 61 90 90 8 9 8 362 53 0 7 66 15 11 14 35 327 61 0 16 74 14 10 13 258 66 1 28 78 14 10 12 30 387 55 0 10 69 15 11 13 25 326 47 0 7 59 17 11 14 Bipolar 20 270 57 0 17 69 17 11 13 1. 60 15 193 44 1 11 53 22 17 18 10 140 69 6 46 77 15 13 12 2.5 5 81 73 17 53 80 15 12 18 1 23 82 38 71 87 10 20 13 5 79 75 19 58 82 14 12 16 29 83 38 75 87 10 20 13 Unipolar 1 0 20 86 42 80 89 9 18 13 180 26 83 37 70 88 11 22 15 Full wave domain : 300-2500 nm; UV light : 300-380 nm; Visible light : 380-780 nm; NIR light : 780-2500 nm

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Pr

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2.5 2 1.5

8 16 14 15 15 18 19 23 16 14 8 13 8 8 9

Journal Pre-proof Table 4 : Analysis of DLC thin films fabricated under various process conditions Sample

Raman PeakD (cm-1)

PeakG (cm)

BP2500W-1min-

1364.6

1542.2

0.673

UP2500W-1min-

1361.4

1542.9

0.648

BP2500W-5min-

1355

1543.9

0.867

UP2500W-5min-

1354.2

pr

1

ID/IG

0.848

UP2500W-1min-

1366.3

UP2500W-1min-

1365.9

B60

oo

f

B60

B60

e-

1545.6

Pr

B60

0.616

1541

0.692

rn Jo u

B180

al

B0

1543.8

BP: bipolar mode, UP: unipolar mode, B: Substrate Bias voltage

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6