Effects of Aging on Chlorinated Plasma Polymers

© 2017 Materials Research. 2017; 20(4): 862-865 DOI: http://dx.doi.org/10.1590/1980-5373-MR-2016-0667 Effects of Aging on Chlorinated Plasma Polymers Rafael Gustavo Turria, Milena Kowalczuk Manosso Amorima, Tayan Vieira Hadicha, Isabela Cristina Fernandesa, Gabriel Ferreira Fernandesa, Diego Rossia, Elidiane Cipriano Rangela, Steven Frederick Durranta* a Laboratório de Plasmas Tecnológicos, Instituto de Ciência e Tecnologia de Sorocaba, Universidade Estadual Paulista - UNESP, Avenida Três de Marco, 511, Alto da Boa Vista, 18087-180, Sorocaba, SP, Brazil Received: September 14, 2016; Revised: November 21, 2016; Accepted: January 03, 2017 Thin films deposited from propanol-chloroform-argon mixtures by plasma enhanced chemical vapor deposition at different partial pressures of chloroform in the feed, CCl, were characterized after two years of aging and their characteristics compared with their as-deposited properties. Film thickness decreased and surface roughness increased with aging. Surface contact angles also increased with aging for the chlorinated films. For the film deposited with 40% chloroform in the feed the contact angle increased about 14°. Transmission infrared and Energy dispersive X-ray spectroscopy revealed that the films gain carbonyl and hydroxyl groups and lose chlorine and hydrogen on aging. Chlorination appears to make the films more durable. Delamination was observed for the unchlorinated films. Keywords: thin films; a-C:H:O:Cl; IRS; stability; contact angle 1. Introduction Although some studies have been made on amorphous hydrogenated carbon films containing chlorine1-3 there is still a relative dearth of literature dealing with such materials. Here, a-C:H:O:Cl films deposited from plasmas fed propanol, chloroform and argon1 and aged for two years are characterized to investigate any morphological, structural and compositional changes. In the present investigation, film thickness and surface roughness were studied using Profilometry. Surface contact angles were measured using goniometry. Chemical structure and composition are examined using Transmission infrared spectroscopy and Energy dispersive X-ray spectroscopy, respectively. Surface features of the aged films were examined using Scanning electron microscopy. 2. Experimental 2.1 Film Production Details of the depositions are given in the literature1. In brief, films were produced by the PECVD of propanolchloroform-argon mixtures at constant total pressure, and partial pressures of chloroform of 0 to 40%. As the proportion of chloroform in the feed was increased the proportion of argon was correspondingly decreased. 2.2 Characterizations Film thickness was measured using a profilometer on samples deposited onto smooth glass plates containing a * e-mail: film step-height delineated during the deposition process with the aid of a mask. Nine horizontal scans of 2000 μm length obtained with a Veeco Dektak 150 profilometer were taken. Surface roughness, Ra, was calculated from these data for each film. Surface wettability was determined from contact angle (θ) data taken using a Ramé-Hart 100 goniometer. These measurements were conducted immediately after deposition and two years later. The samples were stored for ageing under ambient atmospheric conditions for two years. Three drops of deionized water (0.2 µL) were deposited on different regions of the sample surface and the contact angle was measured 10 times on each side of the drop, resulting in sixty θ values per sample. A Jasco FTIR-410 spectrophotometer was used for transmission infrared spectroscopy in the 4000 to 400 cm-1 range. Each spectrum comprised 128 scans; a resolution of 4 cm-1 was achieved. Images of the aged films were obtained using a Jeol JSM-6010LA scanning electron microscope equipped with a secondary electron detector. Chemical composition of the aged films was studied using EDS. 3. Results and Discussion Figure 1 shows the film thickness as a function of the percentage of chloroform in the feed, CCl. The aged films tend to be thinner perhaps owing to the loss of chlorine as discussed below. Decreases of around 10% have been observed in the aging (-40 days) of a-C:H:O films (where a-prefix indicates Effects of Aging on Chlorinated Plasma Polymers Figure 1: Film thickness as a function of CCl for the as-deposited and aged films. amorphous) produced from acetone plasmas4. Apart for the absence of chlorine, these films have chemical compositions similar to the films examined in the present study. For the most chlorinated films in the present study, which were obtained at CCl of 30% and 40%, the relative thickness decreases were roughly 30% and 13%, respectively. The condition of the aged unchlorinated film prevented its thickness from being reliably measured. However, the film deposited at CCl = 10%, and therefore having very low chlorine content, suffered a decrease in thickness of around 8%, compatible with the value of 10% cited above for a-C:H:O films. Figure 2 shows the surface roughness, Ra, as a function of CCl. The aged films are consistently and considerable rougher than the as-deposited material, Ra increasing from around 50 nm to more than 200 nm for the aged films. This may be due to the strong de-chlorination and increase in oxygen-containing functionalities as revealed by the infrared and elemental analyses discussed below. (The roughness of the unchlorinated film could not be reliably measured.) Figure 3 shows the surface contact angle as a function of CCl. There is a clear tendency to greater contact angles with aging for the originally more chlorinated films. For the film deposited at a CCl of 40%, the surface contact angle increases from ~72° to ~86°. The increase in the presence of polar oxygen-containing groups with aging would be expected to decrease the contact angle but the considerable increase in roughness (Figure 2) tends to increase it. The magnitude of the contact angle is similar to those obtained for a-C:H:Cl films containing considerably more chlorine (~45 at.%), for which the contact angles were about 77° 2. Figure 4 shows transmittance spectra of pairs of films (as-deposited and aged) produced at CCl (percentage of chloroform in the feed) of 0, 10, 20, 30 and 40. All spectra show absorptions at 2950, 2900 and 2850 cm-1, respectively, due to CH, CH2 and CH3. Similarly, owing to CH2 and CH3 groups, all the spectra show absorptions centered around 863 Figure 2: Surface roughness as a function of CCl for the as-deposited and aged films. Figure 3: Surface contact angle as a function of CCl for the asdeposited and aged films. 1450 and 1380 cm-1. All spectra also exhibit a characteristic absorption at around 1700 cm-1, attributed to the presence of stretching in C=O groups. Inspection of Figure 4 reveals that the peak heights of the absorptions due to C=O increase in the aged films compared to the peaks due to CHx. The spectra of the aged chlorinated films show a clear absorption at ~108 (...truncated)