Characterization of zinc oxide films deposited in helium–oxygen and argon–helium–oxygen atmospheres by sputtering

    Characterization of zinc oxide films deposited in helium-oxygen and argonhelium-oxygen atmospheres by sputtering Kartik H. Patel, Sushant K. Rawal PII: DOI: Reference:

S0040-6090(16)30555-7 doi:10.1016/j.tsf.2016.08.074 TSF 35496

To appear in:

Thin Solid Films

Received date: Revised date: Accepted date:

21 March 2016 22 July 2016 20 August 2016

Please cite this article as: Kartik H. Patel, Sushant K. Rawal, Characterization of zinc oxide films deposited in helium-oxygen and argon-helium-oxygen atmospheres by sputtering, Thin Solid Films (2016), doi:10.1016/j.tsf.2016.08.074

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ACCEPTED MANUSCRIPT Characterization of zinc oxide films deposited in helium-oxygen and

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argon-helium-oxygen atmospheres by sputtering

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a

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Kartik H. Patela and Sushant K. Rawalb*

CHAMOS Matrusanstha Department of Mechanical Engineering,

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Chandubhai S. Patel Institute of Technology (CSPIT), Charotar University of Science and Technology (CHARUSAT),

b

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Changa-388421, Gujarat, India. McMaster Manufacturing Research Institute, Department of Mechanical Engineering,

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McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4L7, Canada *Corresponding Author E-mail: [email protected]

Abstract:

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TELEPHONE: +1 647 673 8701

Zinc oxide (ZnO) thin films were deposited onto glass substrates by radio frequency (RF) magnetron sputtering using a metallic zinc target. Zinc oxide films were prepared in two different gas atmospheres; in the first set, helium and oxygen gas flow ratio (He:O2) was varied from 87.5% to 37.5%. In the second set of experiment, oxygen flow rate was kept constant at 2.5sccm while argon and helium gas flow ratio (Ar:He) was varied from 9.0% to 87.5%. The structural, wettability and optical properties of ZnO films were investigated by X-ray diffractometry (XRD), contact angle measuring system and UV-vis-NIR spectrophotometer. The XRD results show increased preferred orientation along (002) plane for deposited ZnO films in

ACCEPTED MANUSCRIPT both cases. The average crystallite size of ZnO films increases with increase in gas ratio for both set of experiments. The deposited films are hydrophobic by nature for water and ethylene glycol.

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Optical transmittances greater than 60% were observed in the wavelength interval from 450nm

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to 650nm for both cases.

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Keywords: ZnO; Sputtering; Gas Ratio; Wettability; Hydrophobic; Optical Properties.

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1. Introduction

The interest in ZnO structures has increased in recent years; ZnO has received more

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attention due to its exceptional morphology and dimension dependent properties. ZnO being a

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wide band gap semiconductor (3.3eV) has received more attention as it possesses a wide range of useful properties including electrical, chemical, optical and magnetic properties [1-5]. ZnO thin

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films play an important role in various technological areas, such as transparent conducting thin films/electrodes in display devices & solar cells, piezoelectric devices, vapor gas sensor devices, surface & bulk acoustic wave devices, acoustic optical devices, light-emitting diodes and laser diodes due to their good bond strength, optical quality, extreme stability of exactions and excellent piezoelectric properties [6,7]. ZnO has many potential applications like thin film transistors (TFTs), ultraviolet resistive coatings, gas sensors and mobile phones.

Wettability has substantiated to be an important property of solid surfaces and has subsequently growing research interest in the last few years. Wetting properties can be modified by deploying the morphology and chemistry of any substrate. The control of wettability is very useful for many applications as it would be constructive to be able to modify between

ACCEPTED MANUSCRIPT hydrophilicity and hydrophobicity [8]. Hydrophobicity and transparency are complicated properties that are inversely proportional to each other. Translucent hydrophobic coatings may

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be used in several industrial applications such as anti-rusting, antiwetting, anti-fogging, anti-ice

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adherence and moderated friction resistance coatings [9]. Ethylene glycol is used as a medium

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for convective heat transfer in automobiles [10].

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Helium and argon gas mixture atmosphere are utilized in magnetron sputtering technique to prepare different thin films like WO3 [11], Co-Cr [12], Ti [13], Si [14] etc. The studies

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exploring the effect of different gas atmospheres on ZnO nanostructured thin films are insufficient in literatures. The objective of the current work is to develop transparent

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hydrophobic zinc oxide nanostructured thin films by reactive RF magnetron sputtering. The novelty of this work is aimed to explore specifically the effect of helium plus argon gas mixture

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on structural, optical and wettability properties of ZnO nanostructured thin films. The studies exploring usage of these two inert gases on various properties of ZnO nanostructured thin films are very rare in literatures. The focus is specifically to examine contact angle and contact angle hysteresis for water and ethylene glycol on deposited ZnO films.

2. Experimental details

Custom designed 16” diameter × 14” cylindrical chamber (Excel Instruments, India) was used for preparing ZnO thin films by RF magnetron sputtering. Zinc (Zn) target of 50.8mm diameter was kept at a distance of 50mm from substrate. The deposition was carried out at constant RF power of 150W and deposition temperature of 300°C. ZnO thin films were

ACCEPTED MANUSCRIPT deposited for 60 minutes at deposition pressure of 2.0Pa. ZnO films were prepared in two different gas atmospheres namely helium-oxygen and argon-helium-oxygen atmospheres. Gas

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flow of helium, argon and oxygen were precisely controlled by mass flow controller (Alicat,

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USA). In the first set of experiment for helium-oxygen atmosphere, helium and oxygen gas flow ratio (He:O2) was varied from 87.5% to 37.5% at different values of 87.5%, 75.0%, 62.5%,

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50.0% and 37.5%. Their respective sample names are 87.5, 75.0, 62.5, 50.0 and 37.5. In the

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second set of experiment for argon-helium-oxygen atmosphere, oxygen flow rate was kept constant at 2.5sccm while argon and helium gas flow ratio (Ar:He) was varied from 9.0% to

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87.5%. Ar:He was varied at different values of 9.0%, 26.5%, 44.0%, 61.0% and 87.5% and their

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respective sample names are 9.0, 26.5, 44.0, 61.0 and 87.5.

The structural properties of ZnO nanostructured thin films were studied by X-ray

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diffractometer (Bruker, Model D2 Phaser) using Bragg-Bentano θ-2θ configuration with Cu-Ka radiation having wavelength of 1.54Ǻ. The elemental analysis was done using an energy dispersive X-ray analysis (ZEISS, EVO 18). Atomic force microscopy (Nanosurf easyscan2) in non-contact mode was utilized to characterize its surface topography. The wettability properties of ZnO thin films were done by contact angle measuring system (Ramehart, Model 290). The optical properties of ZnO nanostructured thin films were recorded by UV-vis-NIR spectrophotometer (Shimadzu, Model UV-3600 plus).

3. Results and discussion

ACCEPTED MANUSCRIPT The presence of different phases and their orientations in ZnO films deposited in heliumoxygen and argon-helium-oxygen atmospheres were determined by X-ray Diffraction analysis.

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The XRD pattern of nanocrystalline ZnO thin films deposited in helium-oxygen atmosphere at

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different helium and oxygen gas flow ratio (He:O2) is shown in Fig. 1a. For sample 37.5, ZnO phase with (002) peak and weakly crystalline (100) and (110) peaks are observed. Intensity of

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(100) peak increases for sample 50.0 whereas (002) and (110) peaks are having intensities

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similar to sample 37.5. Samples 62.5 and 75.0 hardly shows any difference in intensities of (002), (100) and (110) peaks. When He:O2 ratio is 87.5% for sample 87.5, the maximum

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intensities for (100) and (002) peaks are observed. Evolution of (101) peak along with weakly

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crystalline (110) peak for ZnO is also observed at this condition.

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The XRD pattern for ZnO films deposited in argon-helium-oxygen atmospheres where

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argon and helium gas flow ratio (Ar:He) is varied from 9.0% to 87.5% is shown in Fig. 1b. When Ar:He ratio is 9.0% for sample 9.0, (100) and (002) peaks of ZnO having lower intensities are observed. Weakly crystalline (100) peak of ZnO is observed further only when Ar:He ratio is 26.5% that is the case for sample 26.5. When Ar:He ratio is further increased from 44.0% to 87.5%, (100) peak disappears and only well intense (002) peak of ZnO is observed for samples 44.0, 61.0 and 87.5 respectively. The XRD spectra exhibit a strong (002) peak which indicates that they have a preferential growth orientation along the c-axis perpendicular to the substrate surface. As the percentage of Ar is increased, the relative intensity of (002) diffraction peak increases gradually. The loss of c-axis preference when He-O2 mixtures is used may be due to the process of penning ionization that occurs in plasma. Helium has highest energy than the first ionization potential of oxygen and therefore it can easily ionize the latter. However argon cannot

ACCEPTED MANUSCRIPT easily ionize oxygen through the penning ionization process due to is lower energy [11,15,16]. So for ZnO films deposited in He-O2 mixtures, there will be more proportion of oxygen atoms

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available that may have resulted in formation of various textures of ZnO films and resulted in

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loss of c-axis preference with evolution of various orientations. When ZnO films are deposited in Ar-O2 mixtures, there may be less oxygen atoms available due to lower ionization potential of

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argon leading to c-axis orientation which is the most preferred orientation for ZnO.

Scherrer formula [17] was utilized to measure average crystallite size “d” of ZnO films.

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The calculated average crystallite size of ZnO films are given in Table 1. The average crystallite size of ZnO films increases from 14nm to 20nm with increase in He:O2 ratio from 37.5% to

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87.5% and from 18nm to 27nm with increase in Ar:He ratio from 9.0% to 87.5%. The film deposited in helium-oxygen atmosphere having smaller crystallite size compared to the ones

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deposited in argon-helium atmosphere can be explained by the mean free path theory [18]. The total atomic radius of helium-oxygen gases is lower as compared to argon-helium-oxygen gases. The increase in size of sputtering gas atoms within the sputtering chamber leads to decrease in the mean free path, thereby increasing their collision frequency. Westwood [19] had discussed the mean free path of an atom with respect to mass and diameter of sputtered atoms and gas atoms. He had obtained a set of curves for the distance an atom has to travel normal to the target before it is thermalized giving due consideration to the mean free path and scattering dynamics of sputtered atoms in the sputtering atmosphere. He concluded that the distance increases with the mass of an atom, its initial ejection energy and with decreasing pressure of the sputtering gas. Helium has a very low mass compared to argon. So when the films are deposited in helium

ACCEPTED MANUSCRIPT atmosphere, the sputtered atoms have to travel a lesser distance to get thermalized as reported by

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Westwood [19].

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Kohl et al studied the impact of Xe+ ion bombardment on ZnO films deposited with and without additional ion bombardment, respectively. Bombardment was done initially at the start

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of deposition process and was stopped after certain duration of time. The time duration was

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different for each deposition process to examine effect of ion bombardment at different growth stages. They found that ZnO films grown with Xe+ ion beam assisted sputtering exhibit structural

properties

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considerably improved

and

crystalline

quality compared

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conventionally sputtered films under otherwise similar conditions. They concluded that ion

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bombardment during the initial stage of film growth only results in the formation of a drastically improved structure and that there is no further improvement for longer durations of ion

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bombardment [20].

When films are deposited in helium-oxygen atmosphere, the sputtered atoms have to travel a lesser distance to get thermalized as reported by Westwood due to lower atomic mass of helium as compared to argon. So the sputtering yield will be lower for films deposited in heliumoxygen atmosphere as compared to films deposited in argon-helium-oxygen atmosphere. Moreover as the diameter of the gas molecule increases, the sputtered atoms would also undergo multiple collisions leading to a higher probability of agglomeration and growth even before arriving at the substrate as reported in literature [21]. The diameter of gas molecules for argonhelium-oxygen atmosphere is larger as compared to helium-oxygen atmosphere. Therefore, the average crystallite size of ZnO films is larger for films deposited in argon-helium-oxygen

ACCEPTED MANUSCRIPT atmosphere as compared to films deposited in helium-oxygen atmosphere. We have studied the stoichiometry of ZnO films by using energy dispersive X-ray analysis. The O/Zn ratio varies

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from 1.33 to 0.96 depending upon the gas mixture. It is observed that with increase of gas

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mixture, the deposited ZnO films becomes stoichiometric and O/Zn ratio values approaches to

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near unity as reported in Table 1.

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Normally to develop good hydrophobic surfaces, the surfaces with microtextures and nanotextures or their mixture are desirable. It has been described that the surface structure and

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roughness height is very significant in accomplishing a hydrophobic and superhydrophobic surface [22]. That is, in addition to contact areas on a rough surface, the size scale of surface

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structures determines the contact angle of liquid droplet on the surface [23]. The smoother the surface, the lesser will be the contact angle and more proportion of nanotextured surfaces, the

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greater will be the contact angle. Surface roughness is related to contact angle by Wenzel [24] equation as given below:

cos W  A cos 

…..(1)

where A is a roughness factor, defined as the ratio of the real and apparent surface areas and  W is a water contact angle for a rough film surface and  is the characteristic water contact angle depending on the interfacial energy between the three phases at the area of contact [25]. So contact angle varies directly with surface roughness. The contact angle and surface energy is related by the Young equation as given below:

 S   SL   L cos

…..(2)

ACCEPTED MANUSCRIPT Where  S ,  SL and  L are surface energy of the solid-vapour, solid-liquid and liquid-vapour interfaces, respectively, and θ is the equilibrium contact angle. The contact angle and surface

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energy are inversely related to each other [26].

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The Atomic force microscopy (AFM) micrographs of ZnO films deposited in heliumoxygen atmosphere and argon-helium-oxygen atmosphere are shown in Fig. 2. The highest

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possible contact angle, which is desirable in many applications, may be achieved by using hemispherically topped asperities with hexagonal packing pattern or by pyramidal asperities with a

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rounded top [27]. It is observed that ZnO films deposited in helium-oxygen atmosphere and argon-helium-oxygen atmosphere have a mixture of hemi-spherically topped asperities and

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pyramidal asperities with a rounded top. This may have imparted greater contact angle values to the deposited ZnO films. The average crystalline size is smaller for ZnO films deposited in

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helium-oxygen atmosphere as compared to films deposited in argon-helium atmosphere as visible from AFM micrographs, which are in agreement with XRD results. The surface roughness increases when He:O2 ratio was increased from 37.5% to 87.5% in helium-oxygen atmosphere and Ar:He ratio was varied from 9.0% to 87.5% in argon-helium atmosphere.

The contact angle was measured for water and ethylene glycol by sessile drop technique with tolerance of ±2°. The variation of water contact angle with respect to surface roughness for ZnO films deposited in helium-oxygen atmosphere and argon-helium-oxygen atmosphere are shown in Fig. 3. As shown in Fig. 3a and 3b, the contact angle is directly proportional to surface roughness. When He:O2 ratio was increased from 37.5% to 87.5%, roughness increased from 23nm to 36nm and contact angle of water and ethylene glycol raised from 92.7° to 104.7° and

ACCEPTED MANUSCRIPT 73.0° to 89.6° respectively. When Ar:He ratio was varied from 9.0% to 87.5%, the roughness of ZnO thin film increased from 24nm to 39nm whereas the contact angle of water and ethylene

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glycol increased from 93.4° to 115.6° and 75.4° to 92.2° respectively.

The uncoated glass substrate had contact angle value of 26°. ZnO films deposited in

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different atmosphere displays a range of hydrophilic and hydrophobic behavior for water and

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ethylene glycol. The maximum contact angle values of ZnO films observed for water and ethylene glycol are 115.6°and 92.2° respectively. So we have successfully demonstrated the

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development of repellent ZnO thin films that can be modified as per the prerequisite of specific

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uses involving water and ethylene glycol.

The wetting behavior of a thin film is not only characterized by static contact angle.

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Contact Angle Hysteresis (CAH) is the variance between the advancing contact angle (θ A) and receding contact angle (θR) that is measured while determining dynamic contact angle. The CAH is associated to surface roughness and adhesion of droplet to the surface [28]. CAH depends on different factors like roughness, chemical heterogeneities, surface deformation, liquid adsorption and retention, molecular rearrangement on wetting and interdiffusion. The values of advancing contact angle (θA), receding contact angle (θR) and CAH for water and ethylene glycol are given in Table 2. When He:O2 ratio varies from 37.5% to 87.5%, CAH of water decreases from 11.3° to 2.1° and for ethylene glycol, a decline of values from 15.1° to 8.7° is observed. CAH for water declines from 10.6° to 1.8° and for ethylene glycol from 14.8° to 8.4° when Ar:He ratio was raised from 9.0% to 87.5%. The increase of surface roughness may cause trap of liquid droplet within the rough surface which eventually might result in an increase of advancing angle values

ACCEPTED MANUSCRIPT as well as decline of receding contact angle values causing an overall decline of CAH. We were able to achieve lowest CAH values of 1.8° and 8.4° for water and ethylene glycol respectively at

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maximum surface roughness value of 39nm for sample 87.5 deposited at Ar:He ratio of 87.5%.

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The liquid gets easily rolled off from surface during this condition when the sample is slightly tilted from horizontal level. This behavior is very useful for glasses which are used in multi-

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storage buildings and vehicles. We found that the magnitude of CAH decreases with increase in

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He:O2 ratio in first case and Ar:He ratio in second case. It may be due to decrease in interaction of water and ethylene glycol droplet with nanostructured zinc oxide films surface having higher

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surface roughness.

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Contact angle depends on surface roughness and it is inversely proportional to surface energy [29]. The surface morphology and chemical composition are challenging factors for

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surface energy of a film. Surface energy was calculated by Wu method and Owens-Wendt (O.W.) method [30]. Surface energy of ZnO thin deposited in helium-oxygen atmosphere and argon-helium-oxygen atmosphere are shown in Fig. 4 and Fig. 5 respectively. The sum of polar (𝛾𝑆𝑝 ) and dispersive (𝛾𝑆𝑑 ) component is known as total surface energy. The total surface energy found by two methods are in good agreement with each other. The value of surface energy measured varies from 23.44 to 17.81mj/m2 for He:O2 atmosphere and 22.82 to 14.64mj/m2 for Ar:He atmosphere as obtained by Wu method. The values of surface energy for He:O2 atmosphere measured within range 20.2 to 12.13mj/m2 and for Ar:He atmosphere, it varies from 18.97 to 9.55mj/m2 obtained by O.W. method. The surface energy of ZnO thin films found by both methods decreases with the increase in He:O2 ratio from 37.5% to 87.5% in first case and Ar:He ratio from 9.0% to 87.5% in second case.

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UV-vis-NIR spectrophotometer was utilized to measure transmittance and absorbance of

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ZnO thin films. The transmission curves for ZnO nanostructured thin films deposited in helium-

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oxygen atmosphere and argon-helium-oxygen atmosphere are shown in Fig. 6. Optical transmittances greater than 60% were observed in the wavelength interval from 450nm to 650nm

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for both cases. Surface roughness correlates hydrophobicity and transparency which are

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competitive properties by nature against each other. For example, reactive sputter deposited ZnO coatings were transparent but not hydrophobic and thermally oxidized coatings were opaque but

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hydrophobic [31]. Higher surface roughness means presence of more sources of light scattering [32]. As surface roughness increases, the transparency of thin film decreases [33]. Surfaces with

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a high roughness commonly show poor mechanical properties than flat surfaces, and this is a crucial problem for the application of high hydrophobic surfaces [34]. It is observed that with

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increase of gas mixture in both cases, the deposited ZnO films becomes thicker due to more availability of atoms resulting in higher surface roughness values and consequently lower transmission values as observed in fig. 6. The model proposed by Manifacier et al. [35] is used to obtain refractive index of ZnO nanostructured thin films from transmission data. It is evident that the refractive index “n” of ZnO nanostructured thin films is around 2.5 for ZnO nanostructured thin films deposited in helium-oxygen atmosphere and argon-helium atmosphere as given in Table 1.

To determine the optical band gap of zinc oxide films, the absorption spectra of the films were recorded as a function of the wavelength. The optical band gap (Eg) of films was calculated from the absorption coefficient (α) using the Tauc relation [36]. As reported in the literatures,

ACCEPTED MANUSCRIPT zinc oxide is direct band gap semiconductor [37, 38]. Fig. 7a and 7b shows the plot of (αhυ)2 versus photon energy hυ for ZnO nanostructured thin films deposited in helium-oxygen

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atmosphere and argon-helium-oxygen atmosphere. The calculated band gap values for ZnO

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nanostructured thin films varies from 3.2eV to 3.27eV for variation in helium-oxygen atmosphere from 37.5% to 87.5% and from 3.22eV to 3.27eV for argon-helium atmosphere from

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9.0% to 87.5%. The observed band gap values of ZnO thin films deposited at various sputtering

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conditions are in good indenture with literatures [39-41].

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4. Conclusion

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ZnO films reveals presence of (100) and (002) peak in helium-oxygen and argon-heliumoxygen atmospheres. In helium-oxygen atmosphere, when He:O2 ratio was increased from

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37.5% to 87.5%, surface roughness increased from 23nm to 36nm and contact angle of water and ethylene glycol elevated from 92.7° to 104.7° and 73.0° to 89.6° respectively. In argonhelium-oxygen atmospheres, when Ar:He ratio was varied from 9.0% to 87.5%,

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roughness of ZnO thin film increased from 24nm to 39nm whereas the contact angle of water and ethylene glycol increased from 93.4° to 115.6°and 75.4° to 92.2° respectively. The maximum band gap value of 3.27eV was observed for both atmosphere conditions. These films can have feasible application as water repellent protective coatings.

5. Acknowledgement

ACCEPTED MANUSCRIPT This work has been supported by AICTE grant number 20/AICTE/RIFD/RPS (POLICYIII) 24/2012-13 sanctioned under Research Promotion Scheme (RPS). We are thankful to Head,

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Dr. K. C. Patel Research and Development Centre (KRADLE) affiliated to Charotar University of Science and Technology (CHARUSAT), Anand, Gujarat, India for granting permission to use

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various equipment’s available in their characterization laboratory. We are thankful to President

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and Provost of CHARUSAT for supporting this research work.

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[40] V. Senay, S. Pat, S. Korkmaz, T. Aydogmuş, S. Elmas, S. Ozen, M. Z. Balbag, ZnO thin film synthesis by reactive radio frequency magnetron sputtering, Appl. Surf. Sci. 318 (2014) 2-5.

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[41] A. Chawla, D. Kaur, R. Chandra, Structural and optical characterization of ZnO nanocrystalline films deposited by sputtering, Opt. Mater. 29 (2007) 995-998.

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Figure 1: XRD patterns of ZnO films deposited in (a) helium-oxygen atmosphere and (b) argon-

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helium-oxygen atmosphere.

Figure 2: AFM images of ZnO films deposited in (a) helium-oxygen atmosphere and (b) argon-

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helium-oxygen atmosphere.

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Figure 3: Contact angle and surface roughness of ZnO films deposited in (a) helium-oxygen atmosphere and (b) argon-helium-oxygen atmosphere.

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Figure 4: Surface energies of ZnO films deposited in helium-oxygen atmosphere calculated by (a) Wu method (b) O.W. method.

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Figure 5: Surface energies of ZnO films deposited in argon-helium-oxygen atmosphere calculated by (a) Wu method (b) O.W. method.

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Figure 6: Optical transmission curves of ZnO films deposited in (a) helium-oxygen atmosphere and (b) argon-helium-oxygen atmosphere. Figure 7: Optical absorption curves of ZnO films deposited in (a) helium-oxygen atmosphere and (b) argon-helium-oxygen atmosphere.

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Figure 1

Figure 2

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Figure 3

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Figure 4

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Figure 5

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Figure 6

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Figure 7

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Table 1. Calculated parameters of ZnO films.

O/Zn

Avg d(XRD)

Band gap

Refractive

Thickness (nm)

name

ratio

(nm)

(eV)

index (n)

by %T data

87.5

1.33

20

3.20

2.51

525

75.0

1.22

18

3.24

2.51

647

62.5

1.12

17

3.25

50.0

1.08

15

3.26

37.5

1.04

14

9.0

1.27

18

26.5

1.17

20

44.0

1.08

23

61.0

1.00

26

87.5

0.96

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897

2.50

1089

3.27

2.50

1254

3.22

2.51

611

3.23

2.51

741

3.24

2.50

953

3.26

2.50

1297

3.27

2.50

1356

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ACCEPTED MANUSCRIPT Table 2. Static and dynamic contact angle and contact angle hysteresis (CAH) of ZnO films.

in nm

EG

Water θA

θR

EG

CAH

θA

θR

Water

EG

82.0

74.5

59.4

11.3

15.1

RI

Name

Water

23 ± 2

92.7

73.0

93.3

75.0

27 ± 2

95.0

77.0

97.6

88.0

80.3

66.9

9.6

13.4

62.5

30 ± 2

97.4

82.3

100.2

93.0

85.7

74

7.2

11.7

50.0

33 ± 2

100.1

86.4

105.3

100.7

90.1

79.5

4.6

10.6

37.5

36 ± 2

104.7

89.6

109.8

107.7

94.8

86.1

2.1

8.7

9.0

24 ± 2

93.4

75.4

94.6

84

77.5

62.7

10.6

14.8

26.5

27 ± 2

96.3

80.3

97.8

90.4

84.8

71.2

7.4

13.6

44.0

32 ± 2

99.6

84.4

104.5

98.7

89.4

77.1

5.8

12.3

61.0

37 ± 2

107.6

88.7

116.3

112.1

92.5

81.7

4.2

10.8

87.5

39 ± 2

115.6

92.2

121.3

119.5

97.7

89.3

1.8

8.4

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87.5

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Dynamic angle (in Deg.)

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Static angle (in Deg.)

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Effect of different gas atmosphere like Ar: He and Ar: He: O2.

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Contact Angle Hysteresis & Wettability studies for ZnO surfaces.