Microstructure and micromorphology of ZnO thin films: Case study on Al doping and annealing effects

Accepted Manuscript Microstructure and Micromorphology of ZnO Thin Films: Case Study on Al Doping and Annealing Effects Ştefan Ţălu, Miroslaw Bramowicz, Slawomir Kulesza, Shahram Solaymani, Atefeh Ghaderi, Laya Dejam, Seyed Mohammad Elahi, Arash Boochani PII:

S0749-6036(16)30096-9

DOI:

10.1016/j.spmi.2016.03.003

Reference:

YSPMI 4231

To appear in:

Superlattices and Microstructures

Received Date: 1 March 2016 Accepted Date: 2 March 2016

Please cite this article as: Ş. Ţălu, M. Bramowicz, S. Kulesza, S. Solaymani, A. Ghaderi, L. Dejam, S.M. Elahi, A. Boochani, Microstructure and Micromorphology of ZnO Thin Films: Case Study on Al Doping and Annealing Effects, Superlattices and Microstructures (2016), doi: 10.1016/j.spmi.2016.03.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Microstructure and Micromorphology of ZnO Thin Films: Case Study on Al Doping and Annealing Effects

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Ştefan Ţălu 1, Miroslaw Bramowicz 2, Slawomir Kulesza 3, Shahram Solaymani4, Atefeh Ghaderi4,*, Laya Dejam5, Seyed Mohammad Elahi5, Arash Boochani6 1

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Technical University of Cluj-Napoca, Faculty of Mechanical Engineering, Department of AET, Discipline of Descriptive Geometry and Engineering Graphics, 103-105 B-dul Muncii St., ClujNapoca 400641, Cluj, Romania. 2 University of Warmia and Mazury in Olsztyn, Faculty of Technical Sciences, Oczapowskiego 11, 10-719 Olsztyn, Poland. 3 University of Warmia and Mazury in Olsztyn, Faculty of Mathematics and Computer Science, Sloneczna 54, 10-710 Olsztyn, Poland. 4 Young Researchers and Elite Club, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran. 5 Plasma Physics Research Centre, Science and Research Branch, Islamic Azad University, Tehran, Iran 6 Physics Department, Islamic Azad University Kermanshah Branch, Kermanshah, Iran.

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Corresponding author *: Atefeh Ghaderi Young Researchers and Elite Club, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran. Phone: +989187204944 E-mail: [email protected]

Abstract

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Declaration of interest: The authors declare no conflict of interest. Authors alone are responsible for the content and opinions expressed in this article.

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The aim of this work is to investigate the three-dimensional (3-D) surface texture of Aliminium doped Zinc Oxide (AZO) thin films deposited by Radio Frequency sputtering method on the quartz substrates. Deposited samples were annealed under argon flux at three different temperatures: 400 ºC, 500 ºC, and 600 ºC, followed by gradual cooling down to room temperature. To characterize the structures of samples Powder X-ray diffraction patterns and Rutherford Back Scattering (RBS) spectra were applied. The Scanning electron microscope (SEM) and the atomic force microscope (AFM) were applied to study the samples’ surface morphology. Then statistical, fractal and functional surface characteristics were computed. The analysis of 3-D surface texture of AZO thin films is crucial to control the 3-D surface topography features and to correct interpretate the surface topographic parameters. It also allows 1

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understanding the relationship between 3-D the surface topography and the functional (physical, chemical and mechanical) properties of AZO thin films. Key words: AZO thin films, Radio Frequency sputtering, AFM, Fractal Analysis, ThreeDimensional Surface micromorphology.

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1. INTRODUCTION

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Over last few decades, Aluminium doped zinc oxide thin films were prepared by a variety of techniques such as: evaporation, Pulsed Laser Deposition (PLD), chemical deposition, Metal Organic Chemical Vapor Deposition (MOCVD), spray pyrolysis and magnetron sputtering [1,2]. Among these techniques magnetron sputtering is particular interesting, since it is offering low temperature deposition, robust process, repeatability, uniformity and large area fabrication adaptability [3]. Sputtered AZO is a degenerated, semiconductor and a wide band gap conductive oxide (mainly due to defect - nonstoichiometry - or dopant controlled n-type carrier concentration [4]), that offer high transparency in the visible range, owing to a large intrinsic band gap (~3 eV), combined with a tunable conductivity [3]. The 3-D surface morphology of thin films plays a major role in nanotribology and thermodynamics of interconnected layers and nanostructures at microscopic and macroscopic length scales [5-9]. The complex surface nanoscale interactions in a tribological interface require an extensive knowledge on the relationships of physical and mechanical models of nano structures at the atomic scale/resolution, especially when very large quantities of digital data are generated in high-resolution models [10-15]. These 3-D models can be applied in studies of surface chemistry, nucleation and growth phenomen at the nanoscale in connection with statistical mechanics [16-20]. In practical engineering, the 3-D engineering surface textures can be classified as isotropic (Gaussian or non-Gaussian) or anisotropic [21-23]. The information of anisotropic topography is related to anisotropy between form, waviness and roughness; and the local anisotropy of 3-D motifs [24]. In other works, the topographic features and the surface patterns of thin films at 3-D nanoscale was studied from the height images by atomic force microscopy (AFM) [25], using fractal [7, 9, 15-20] and multifractal [10-12, 20] geometry. It is known the statistical self-similarity of fractal 3-D surfaces of thin films appear over a restricted range of length scales [21, 23, 26]. The aim of this study is to synthesize the AZO thin films by RF sputtering method on the quartz substrates, and to study their 3-D surface texture using AFM data in connection with the statistical, and fractal analyses, to elucidate the 3-D fractal patterns of the heterogeneous components. 2. MATERIALS AND METHODS 2.1. Materials and preparation of thin films AZO target was utilized with high purity of Zn (Sun Metals Grade-Spacial High Grade (SHG)) and Al 99.99% purity (Merck) to deposit Al:ZnO (AZO) on quartz substrates. The target was 2

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#1 #2 #3 #4

AZO AZO AZO AZO

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Table 1. The ID and technical sputtering details of samples Sputtering parameters Annealing Temperature (ºC) Basic pressure [N/m2] Work pressure [N/m2] 2×10-3 78×10-2 As Deposited -3 -2 2×10 78×10 400 2×10-3 78×10-2 500 -3 -2 2×10 78×10 600

2.2. Characterization of thin films

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circle-shape with diameter of 77 mm and thickness of 3 mm, Al weight ratio was ~10(%) and that of Zn was 90%. To deposit AZO films, the RF sputtering system with the constant O2 ( O2 + Ar ) ratio of 30% and power of 125W was applied. Base pressure was 2×10-3 N/m2 with the initial vacuum of 78×10-2 N/m2. Substrates were pre-sputtered during 30 min to remove possible oxide residues followed by film deposition at room temperature. Then, the prepared samples were annealed at three different temperatures of 400 ºC, 500 ºC, and 600 ºC during 60 min with the rate of 10ºC/min under argon flux and cooled down gradually to room temperature. The technical sputtering details of samples are given in Table 1.

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Scanning Electron Microscopy (SEM), VEGA-TESCAN LMU in EDX mode, were employed to scan the target surface that showed the great harmony of weight ratio of Al in the target with the average of ~10%. The surface topography and roughness of the samples were recorded using an Autoprobe M4 atomic force microscope (Veeco, Santa Barbara, CA) equipped with ProScan V1.51b software (Veeco). Images were acquired in non-contact mode over square areas of 1 µm × 1 µm with a standard tipped CSC12 cantilever of 0.03 N/m nominal stiffness (Veeco). The experiments were carried out at room temperature (24 ± 1°C). A FESEM ZEISS SIGMA-VP field emission scanning electron microscope was used to take FESEM images at very high vacuum condition. To identify the crystal structure of AZO thin films, STOE-XRD diffractometer using CuKα line (λ = 0.15406 nm) was used. Photo luminescence (PL) was utilized to point out luminescence characteristics of thin films by Cary Eclipse spectrometer equipped with a xenon lamp with 320 nm excite wavelength. By using SIMN RA software [27] the simulation of obtained spectra from Rutherford Back Scattering (RBS) spectra has been done in which the 2.0 MeV He+ ions and detectors located at 162° with resolution of 15 keV.

2.3. Characterization of the film surface texture

Surface texture analysis starts from extracting residual surface, which is the surface remaining after subtraction of the waviness from raw AFM height data. Then, after averaging of the AFM images with their lagged copies, the Areal Autocorrelation Function (AACF) can be calculated according to [28, 29]: 3

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R ( τx , τ y ) =

( z ( x, y ) − z ) ⋅ ( z ( x + τ , y + τ ) − z ) x

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(1) S2q Where: <...> denotes the mean value, Sq – is the root mean square surface roughness, whereas (τx, τy) – a vector of a discrete spatial lag. Surface texture ratio Str can be derived from the AACF as the ratio of extreme autocorrelation decay lengths τa along which the normalized AACF drops from 1.0 to 0.2 (Fig. 1A): τ 0 < Str = a1 ≤1 (2) τa 2 R =1→0.2 Where: a1, and a2 – specify the axes of the fastest and the slowest AACF decays, respectively [35]. For Str > 0.5 the surface is said to be isotropic, while for Str < 0.3 – strongly anisotropic. The plot of the AACF is also useful in determination of the grain dimension. To this end, the half-widths of the AACF curve at its half maximum along these extreme directions can be taken as the grain radii Ra1 and Ra2, respectively, the sum of which gives the average grain diameter (Fig. 1a): Dgrain = R a1 + R a 2 (3) Assuming that residual surface is stationary, the Structure Function (SF) can be computed making use of the formula [30]: (4) S ( τx , τy ) = 2Sq2 1 − R ( τx , τy )

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By plotting averaged structure function on a double logarithmic scale, fractal dimension D and corner frequency fc can be derived.

(a) (b) Fig. 1. (a) AACF plot showing decay lengths τa1, τa2 and grain radii Ra1, Ra2 along the directions of the shortest and the longest AACF decays, respectively; (b) plot of the Firestone-Abbott curve explaining main functional characteristics of the surface. Functional parameters can be derived from the Firestone-Abbott curve (Fig. 1b) also known as the bearing curve. The curve is based on a series of height data arranged in a descending order and plotted on the percent scale, where 100 % corresponds to the lowest sample in the series.

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2.4. The Minkowski functionals

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DIN 4776 standard specifies several characteristics that can be useful in describing topographical complexity of the surface that includes (Fig. 1b): a) kernel roughness depth Sk – thickness of the core at the flattest part of the bearing curve where the largest increase in material exists; b) reduced peak height Spk, reduced valley depth Svk – thickness of the bearing curve above/below the core profile, respectively; c) upper bearing area Mr1, lower bearing area Mr2 – intersection points of horizontal lines plotted from both ends of the flattest tangent of the bearing curve with that curve that delimit peaks and valleys from the core, respectively; d) surface bearing index Sbi – the ratio of the RMS roughness over the surface height at 5% of the bearing curve; e) core fluid retention index Sci – the ratio of the void volume of the unit sampling area at the core zone over the RMS roughness; f) valley fluid retention index Svi – the ratio of the void volume of the unit sampling area at the valley zone over the RMS roughness.

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Minkowski functionals (MFs) are stereological estimators in the field of stochastic geometry and can be used to provide local and global morphological information of 3-D spatial structures in materials science [31, 32, 33]. Let’s consider the MFs defined for a convex, compact set K ⊂ R3 via Steiner’s formula [34]. Let K ⊕ Br be the dilation of the set K by a closed ball of radius r centered on the origin. The volume V of K ⊕ Br can be expressed as a polynomial function of r as follows [34]: 3 3 (5) V ( K ⊕ Br ) = ∑  Wk ( K ) r k k =0  k  where Wk is the k th Minkowski functional. This definition can be extended to the interior An0 of a compact n-dimensional geometrical object An in 3-D space as follows [34]:

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(6) Wk ( An0 ) = ( −1) 3+ n + k Wk ( A) The local and global morphological information was investigated with a set of MFs [32], that includes volume V, surface S and Euler-Poincaré characteristic (or connectivity number χ). This set was computed and plotted using the Gwyddion 2.28 software [35] according to the following formulas: V = N white / N ; S = N bound / N ; χ = (C white − Cblack ) / N (7) where: N - the total number of pixels; Nwhite - the number of ‘white’ pixels, that is pixels above the threshold (pixels below the threshold are referred to as ‘black’); Nbound - the number of whiteblack pixel boundaries; Cwhite and Cblack - the number of continuous sets of white and black pixels respectively.

2.5. Statistical Analysis The GraphPad InStat version 3.20 computer software package (GraphPad, San Diego, CA, USA) was used for statistical analyses. No significant micrograph and no sample effects (P < 0.05) 5

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were observed in an analysis of variance (ANOVA), followed by a post-hoc Tukey's test between the different examined surface regions.

3. Results

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EDX analysis of prepared AZO target is shown in Fig. 2.

Fig. 2. EXD analysis of prepared Al/Zn target.

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The three dimensional AFM images, for 1 µm × 1 µm as scanning square areas, of the AZO film surfaces deposited on the quartz substrates at: (a) As-deposited sample, sample annealed at (b) 400 ˚C, (c) 500 ˚C and (d) 600 ˚C are presented in Fig. 3 (a-d).

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Fig. 3. AFM scans of the residual surface of AZO thin films: (a) As-deposited sample, sample annealed at (b) 400 ˚C, (c) 500 ˚C and (d) 600 ˚C.

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To determine the distribution and size of nanoparticles on the samples’ surface, typical Field Emission SEM images of samples #1 and #3 (in different scales) was applied which are shown in Fig. 4.

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(c) (d) Fig. 4. Typical FESEM micrographs of samples in two different scales: As-deposited sample in the scale of (a) 100 nm, (b) 20 nm, and sample annealed at 500 ˚C in the scale of (c) 100nm, (d) 20 nm.

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XRD pattern of AZO thin films with various annealing temperatures are shown in Fig. 5.

Fig. 5. XRD pattern of AZO thin films with various annealing temperatures.

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A summary of XRD results of AZO films are shown in Table 2.

Sample #1

#2 #3 #4

Table 2. XRD results of Angle (2θ) Lattice (degree) constant 31.35 A = 3.29 36.69 C = 4.9 33.87 A = 3.18 36.89 C = 5.29 31.44 A = 3.28 8

AZO films FWHM Grain size (degree) (nm) 0.4076 13.7 1.065 0.2585 18 0.8209 0.020 39

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57.50

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A summary of photoluminescence (PL) spectroscopy of AZO thin films with different annealing temperatures are shown in Fig. 6.

Fig. 6. PL analysis of AZO thin films with different annealing temperatures.

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The Rutherford Back Scattering analysis of AZO thin film is shown in Fig. 7.

Fig. 7. Typical RBS analysis of AZO thin film.

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Main statistical and fractal characteristics of samples are written in Table 3.

Str

D

K

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0.89 0.76 0.78 0.98

2.20 2.31 2.38 2.31

5.53·10-3 1.86·10-3 1.19·10-4 2.16·10-4

τs [nm] 36 54 87 100

Sq [nm] 3.64 4.04 1.70 2.12

DAACF DGD [nm] [nm] 53.8 46.1 73.3 76.2 107.5 127.0 123.3 132.4

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Table 3. Statistical and fractal surface properties of prepared samples that involve: Str – surface anisotropy ratio, D – fractal dimension, K – pseudo-topothesy, τs – corner frequency, Sq – RMS surface roughness, DAACF – grain diameter from the AACF, DGD – particle dimension from the particle density.

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Table 4 summarizes main functional parameters concerning surface texture.

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Sk [nm] 8.19 10.72 4.37 5.69

Spk [nm] 12.67 6.85 3.05 4.35

Svk [nm] 13.03 11.43 3.87 3.46

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Table 4. Functional surface properties of prepared samples that involve: Sk – kernel roughness depth, Spk – reduced peak height, Svk – reduced valley depth, Mr1/Mr2 – upper/lower bearing area, Sbi – surface bearing index, Sci – core fluid retention index, Svi – valley fluid retention index.

Mr1 [%] 12.53 9.54 9.66 10.66

Mr2 [%] 90.94 90.91 90.29 94.31

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0.61 0.63 0.62 0.56

0.43 0.37 0.91 0.82

0.03 0.03 0.07 0.04

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Figs. 8, 9 and 10 show the MFs, functions V(z), S(z), and c(z), plotted for the scanning square areas of 1 µm × 1 µm of AZO thin films: a) #1, b) #2, c) #3, and d) #4, (according to Fig. 3). These functions have no units.

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(d) Fig. 8. The Minkowski volume V(z) [no unit] for the scanning areas of 1 µm × 1 µm of: (a) #1, (b) #2, c) #3, and d) #4

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Fig. 9. The Minkowski surface S(z) [no unit] for the scanning areas of 1 µm × 1 µm of: (a) #1, (b) #2, c) #3, and d) #4

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Fig. 10. The Minkowski connectivity c(z) [no unit] for the scanning areas of 1 µm × 1 µm of: (a) #1, (b) #2, c) #3, and d) #4

4. DISCUSSION

According to Fig. 2 the EDX analysis shows the content of prepared AZO target. The EDX pattern confirms that Al weight ratio is ~10% and that of Zn is 90%. Fig. 3 shows orthogonal projections of AFM scans of the films taken over 1 µm2 square areas. In general, samples exhibit flat residual surfaces with a number of fine and homogeneous spread grains. Table 3 summarizes main statistical properties of the AZO films derived from AFM images. 13

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In the beginning, number of particles per square area approaches the largest value 4.7×1010 cm-2 for the as-deposited sample, and then gradually decreases to 1.7×1010 cm-2, 6.2×109 cm-2, and finally 5.7×109 cm-2 for samples annealed at, respectively, 400 ˚C, 500 ˚C, and 600 ˚C. Assuming that particles are squares covering entire scan area, corresponding particle dimensions DGD turn out to rise approaching, respectively, 46.1, 76.2, 127.0, and 132.4 nm. Note that AACF gives similar results: 53.8, 73.3, 107.5, and 123.3 nm and the relative error between these two methods is not higher than 18 per cent. Unlike increasing in-plane particle dimension, vertical particle size steadily falls down from 35 nm for the as-deposited sample to around 13 nm for the sample annealed at 600 ˚C. Decreasing particle height is correlated with decreasing surface roughness, which goes from 3.64 nm for the as-deposited sample down to 2.12 nm for the sample annealed at 600 ˚C. Combining these results together it turns out that the annealing step results in larger but flatter AZO particles as if they get smeared over the surface. As can be seen from AFM images of the as-deposited AZO films, the particle size and shape are not clear, while by increasing annealing temperature, they become distinguishable. By increasing temperature to 600 ºC, AZO particles became almost spherical. Due to high content of Al in AZO target, which was 10% weight ratio, doping plays a great role in the subject. As can be seen from typical field emission SEM images shown by Fig. 4 the mean approximate size of nanoparticles is less than 50 nm for both samples #1 and #3. The XRD pattern of AZO thin films is shown in Fig. 5. It could be observed that there is no noticeable peak in as-deposited AZO which indicated the amorphous property of the film. AZO annealed thin film at 400 ˚C shows two different peaks at 31.35 and 36.69 degree corresponds to (100) and (101), which are related to hexagonal structure of ZnO, respectively. More annealing to 500 ˚C shows preferential orientation in (002) at 33.87 degree and a small peak at 36.89 degree related to (101). By increasing temperature to 600 ˚C, two peaks are observable at 31.44 and 57.50 degrees corresponds to (100) and (110), also are related to hexagonal structure of ZnO, respectively. Besides, the second peak intensity of AZO film annealed at 600 oC is more than that of the other one. By considering the deposition conditions such as the ratio of oxygen to argon (3:7), the as deposited thin films do not have any crystalline preferential orientation. While, after post annealing, trapped oxygen atoms between grain boundaries will be evaporated so, AZO grains surfaces’ energy increased, then a small crystalline orientation with low intensity can be observed at 400 ˚C. The c-axis orientation growth due to improvement of stoichiometry is resulted from annealing at 500 ˚C. On the contrary, by annealing to 600 ˚C, lattice mismatch happens following from stoichiometry disturbance. According to Table 2 which reports the XRD analysis details of AZO films, the grain size is increased by increasing annealing temperature which could lead to disturbance of grain boundaries resulting in sticking grains to one another as being annealed [36]. By increasing the annealing temperature the grain size increases. This modification is also observed in AFM images. Photoluminescence result of AZO film is presented in Fig. 6. For better understanding PL, Gaussian fitting is performed for all samples. It is indicated that four different peaks at 371 nm, 400 nm, 430 nm and 453 nm are obtained for as-deposited AZO pertained to UV, violet, violet 14

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and blue emission, respectively. However, by annealing at different temperatures, one violet peak is added. It is depicted that green emission is not observed in AZO films. Never the less, no green emission was traced in AZO films due to the fact that all deposited films were annealed by argon as a non-reactive gas. It is worth mentioning that green emission was attributed to oxygen vacancies or anti site defects [37, 38]. Therefore, the obtained peaks in PL could show the high quality of films. The RBS analysis (Fig. 7) detected Aluminum, Zinc, and Oxygen nuclei. The details of peaks extracted from SIMN-RA software are as follows: The steps at 580, 655 and 715 keV are correspondence respectively with oxygen, aluminum and zinc nuclei of thin film. Apart from that, Table 3 also confirms that analyzed samples are highly isotropic (anisotropy ratio Str higher than 0.76), which means that their topographical features are roughly independent of the observation axis. Highest anisotropy ratio (0.98) found for the sample annealed at 600 ˚C demonstrates its almost perfect isotropicity. Fractal parameters presented in Table 3 establish self-affine behavior of variations in the surface height at different wavelengths governed by the power-law dependence. As a rule, all the samples exhibit monofractal structure with only one characteristic scan length, referred to as the corner frequency τs, beyond which the above power-law scaling behavior disappears. It agrees well with AFM images in Fig. 3 showing separated particles that do not agglomerate into larger clusters. Note that the corner frequency, although generally 20 - 30 nm smaller, varies similar to the grain dimension DAACF. On the other hand, fractal dimension D, which describes the exponent of the above dependence, is found quite low in the range of 2.20 - 2.38 characteristic of poorly developed surfaces with smooth grains. Table 4 summarizes main functional parameters derived from the Firestone-Abbott curve shown schematically in Fig. 1b. Note in the beginning that the sum of the following parameters, namely: kernel roughness depth Sk, reduced peak height Spk, and reduced valley depth Svk, estimates the thickness of the residual surface equal to: 33.9 nm, 29.0 nm, 11.3 nm, and 13.5 nm, for the samples #1 to #4, respectively, being closely related to the film heights seen in Fig. 3. Unfortunately, apart from observed decrease in obtained parameters and hence the particle heights with increasing annealing temperature, each of these parameters vary in a hardly predictable manner. According to definition, Sk establishes the working base of the residual surface for a long-term tribological behavior. In that aspect, AZO films annealed at 500 and 600 ˚C demonstrate their higher mechanical resistance and load-carrying capacity upon contact with other surfaces. On the other hand, reduced peak height Spk, which defines the thickness of the outer layer being exposed to mechanical damage, vanishes from 12.67 nm (sample #1) to 4.35 nm (sample #4). Basically, the lower Spk goes hand in hand with shorter running-in time, hence, films annealed at the two highest temperatures exhibit larger potential for tribological applications. The above findings agree with the values for upper bearing area Mr1, which specifies the ratio of the peak area to the entire surface height. Studied films exhibit Mr1 in the range between 9.54 and 12.53 per cent. Likewise, reduced valley depth Svk estimates the depth of the valleys on the surface left behind the wearing process that might serve, among others, as lubrication channels. As seen in Table 4, Svk decreases with increasing annealing temperature from 13.03 nm (sample #1) to 3.46 nm (sample #4). Proper fluid retention requires as large Svk value as possible, whereas Svk appears comparable to Sk that actually demonstrates deterioration in these characteristics of the AZO films caused by the annealing. It is confirmed by lower

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bearing index Mr2, which depicts the ratio of the valleys to the entire residual surface height, and slightly varies between 90.29 and 94.31 per cent. Another functional measure of the surface topography is the surface bearing index Sbi. In case of studied AZO films this parameter varies between 0.56 and 0.63, whereas 0.61 is specific of perfect Gaussian surfaces. The last two indices: core fluid retention Sci and valley fluid retention Svi, show even larger deviation of the analyzed surfaces from Gaussian ones. The former fluctuates in a wide range from 0.37 to 0.91 (1.56 for Gaussian surfaces), and the latter takes the value in the range 0.03 to 0.07, which actually equals a half of that specific of Gaussian surfaces (0.11). The specific 3-D nanoscale structural characteristics expressed with MFs - the functions V(z), S(z), and c(z) - allowed a reasonable good prediction of the 3-D pattern corresponding to the size of the structural units which are relevant for a systematically investigation of the relation of topology and effective surface properties.

5. CONCLUSIONS

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REFERENCES

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The objective of this study was the micromorphology analysis of AZO thin films deposited by Radio Frequency sputtering method on the quartz substrates. The characterizations were performed using X-ray diffractometer, ion beam analysis, SEM, AFM, and fractal analyses. Our results also suggest that AFM, statistical, fractal and functional surface properties of AZO thin films can contribute to obtain local and global structural information from regions and for a correct interpretation of surface topographic features as well as its functional role that affect their physical integrity and long-term stability. Furthermore, 3-D surface micromorphology parameters and fractal analysis provide a convenient tool for assessing optimal surface characteristics of thin films. The MFs are predictive tools to quantify 3-D morphological properties and topological information of 3-D surface patterns of thin films. The 3-D surface texture of nanostructures estimated by specific parameters can be included in mathematical models to describe nonlinear processes involved at nanometer scale resolution of thin films. These results can be applied in thermodynamics of thin films in studies of surface diffusion, thermal energy fluctuations, configuration entropy at the nanoscale, and the interfacial dynamics of the layers.

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oxide films, Phys. Rev. B Condens. Matter Mater. Phys., 77, 2008. DOI: 10.1103/PhysRevB.77.115215. 5. Ţălu Ş., Stach S., Ghodselahi T., Ghaderi A., Solaymani S., Boochani A., Garczyk Ż. Topographic Characterization of Cu–Ni NPs @ a-C:H Films By AFM and Multifractal Analysis. J Phys. Chem. B, 119 (17): 5662-5670, 2015. 6. Stach S., Garczyk Z., Ţălu Ş., Solaymani S., Ghaderi A., Moradian R., Nezafat N., Elahi S. M., Gholamali H. Stereometric Parameters of the Cu/Fe NPs Thin Films, J. Phys. Chem. C., 119(31), 17887-17898, 2015. 7. Pelliccione M., Toh-Ming Lu, Evolution of thin film morphology: modeling and simulations. 1st ed., pp. 11-12. Berlin Heidelberg: Springer-Verlag: 2008. 8. Wasa K., Kitabatake M., Adachi H, Thin film materials technology: sputtering of control compound materials. Co-published by: William Andrew, Inc. Norwich, NY, USA and SpringerVerlag GmbH & Co., Heidelberg, Germany: 2004. 9. Duparré A., Ferre-Borrull J., Gliech S., Notni G., Steinert J., Bennett J.M., Surface characterization techniques for determining the root-mean-square roughness and power spectral densities of optical components. Appl Opt. 41(1): 154-171, 2002. 10. Ţălu Ş., Stach S., Solaymani S., Moradian R., Ghaderi A., Hantehzadeh M.R., Elahi S.M., Garczyk Ż., Izadyar S. Multifractal Spectra of Atomic Force Microscope Images of Cu/Fe Nanoparticles Based Films Thickness. J Electroanal. Chem., 749: 31-41, 2015. 11. Wan-Yu Wu, Chia-Hao Wu, Bo-Hong Xiao, Ting-Xin Yang, Shi-Yi Lin, Ping-Hung Chen, Chi-Lung Chang., Microstructure, mechanical and tribological properties of CrWN films deposited by DC magnetron sputtering, Vacuum 87 ,209-212, 2003. 12. Pankiew A., Bunjongpru W., Somwang N., Porntheeraphat S., Sopitpan S., Nukaew J., Hruanun C., Poya A., Study of TiN films morphology deposited by DC magnetron sputtering in different N2:Ar mixtures, Journal of the Microscopy Society of Thailand, 24(2): 103-107, 2010. 13. Reyes-Vidal Y., Suarez-Rojas R., Ruiz C., Torres J., Ţălu Ş., Méndez A., Trejo G. Electrodeposition, characterization, and antibacterial activity of zinc/silver particle composite coatings. Appl Surf Sci. 342: 34-41, 2015. 14. Elenkova D., Zaharieva J., Getsova M., Manolov I., Milanova M., Stach S., Ţălu Ş. Morphology and Optical Properties of SiO2-Based Composite Thin Films with Immobilized Terbium(III) Complex with a Biscoumarin Derivative. Int. J. Polym. Anal. Charact. 20(1): 4256, 2015. 15. B. Bhushan, H. Fuchs, S. Kawata, applied scanning probe methods V, DOI 10.1007/b136626, Springer-Verlag Berlin Heidelberg 2007, PP 149-220. 16. Ramazanov S., Ţălu Ş., Sobola D., Stach S., Ramazanov G. Epitaxy of silicon carbide on silicon: Micromorphological analysis of growth surface evolution. Superlattices and Microstructures, 2015. DOI: 10.1016/j.spmi.2015.08.007. 17. Ţălu Ş., Bramowicz M., Kulesza S., Shafiekhani A., Ghaderi A., Mashayekhi F., Solaymani S. Microstructure and Tribological Properties of FeNPs@a-C:H Films by Micromorphology Analysis and Fractal Geometry, Ind. Eng. Chem. Res., 2015. DOI: 10.1021/acs.iecr.5b02449. 18. Stach S., Roskosz S., Cybo J., Cwajna J. 2009. Properties of sialon ceramics evaluated by means of multifractal, surface stereometry and quantitative fractography techniques. Mater. Charact., 60: 1151-1157, 2009.

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19. Ţălu Ş., Patra N., Salerno M. Micromorphological characterization of polymer-oxide nanocomposite thin films by atomic force microscopy and fractal geometry analysis. Progress in Organic Coatings, 89: 50-56, 2015. 20. Yadav R.P., Kumar M., Mittal A.K., Pandey A.C. Fractal and multifractal characteristics of swift heavy ion induced self-affine nanostructured BaF2 thin film surfaces. Chaos, 25: 083115, 2015. DOI: 10.1063/1.4928695. 21. Bramowicz M., Kulesza S., Lipiński T., Szabracki P., Piątkowski P. Fractal analysis of AFM data characterizing strongly isotropic and anisotropic surface topography, Solid State Phenomena, 203-204: 86-89, 2013. 22. Ţălu Ş. PhD. Thesis: Researches concerning the cold rolling process of external cylindrical threads, Technical University of Cluj-Napoca, Cluj-Napoca, Romania, 1998. 23. Kulesza S., Bramowicz M. A comparative study of correlation methods for determination of fractal parameters in surface characterization. Appl. Surf. Sci. 293: 196-201, 2014. 24. Zahouani H. Spectral and 3D motifs identification of anisotropic topographical components. Analysis and filtering of anisotropic patterns by morphological rose approach. Int. J. Mach. Tools and Manufacturing 38(5-6): 615-623, 1998. 25. Bramowicz M., Kulesza S., Rychlik K. Comparison between contact and tapping AFM modes in surface morphology studies, Technical Sciences, 15(2): 307-318, 2012. 26. Ţălu Ş. Mathematical methods used in monofractal and multifractal analysis for the processing of biological and medical data and images. Anim. Biol. Anim. Husb. 4(1): 1-4, 2012. 27. SIMNRA By Mayer, M.; Developed Since. Max-Planck-Institute for Plasma Physics. Germany, 1996. 28. Nayak P.R. Random process model of rough surfaces, J. of Lubrication Tech. 93(3): 398407, 1971. DOI: 10.1115/1.3451608. 29. Dong W.P., Sullivan P.J., Stout K.J. Comprehensive study of parameters for characterizing 3-dimensional surface topography. 4. Parameters for characterizing spatial and hybrid properties. Wear, 178: 45-60, 1994. 30. Thomas A., Thomas T.R. Digital analysis of very small scale surface roughness, Journal of Wave Material Interaction, 3: 341-350, 1988. 31. Arns C.H., Knackstedt M.A., Mecke K.R., Characterising the morphology of disordered materials. In: K.R. Mecke, D. Stoyan (Eds.): LNP 600, Springer-Verlag Berlin Heidelberg, 37– 74, 2002. 32. Ţălu Ş. Characterization of surface roughness of unworn hydrogel contact lenses at a nanometric scale using methods of modern metrology. Polym. Eng. Sci., 53(10): 2141-2150, 2013. 33. K. Jacobs, R. Seemann, K. Mecke, Dynamics of Structure Formation in Thin Liquid Films: A Special Spatial Analysis. In: K.R. Mecke and D. Stoyan (Eds.): LNP 554, Springer-Verlag Berlin Heidelberg, 2000, 72–91. 34. Charemza M., Thnnes E., Bhalerao A., Parr. D. Geometry descriptors for characterizing emphysema and lung fibrosis in hrct images, In: First International Workshop on Pulmonary Image Processing (MICCAI 2008), New York City, USA, 155–146, 2008. 35. Gwyddion software user guide, version 2.28, 2012 © P. Klapetek, D. Nečas, C. Anderson, Czech Metrology Institute, Brno, Czech Republic (http://gwyddion.net/). 36. Lin Y., Xie J., Wang H., Li Y., Chavez C., Lee S., Foltyn S.R., Crooker S.A., Burrell A.K., McCleskey T.M., Jia Q.X. Thin Solid Films, 492(1-2): 101-104, 2005. 18

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37. Studenikin S.A., Cocivera M., Kellner W., Pascher H. Journal of Luminescence, 91(3–4): 223-232, 2000. 38. Irimpan L., Ambika D., Kumar V., Nampoori V.P.N., Radhakrishnan P. Journal of Applied Physics, 104(3): 033118, 2008.

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Table of Content:

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ACCEPTED MANUSCRIPT - We characterized three-dimensional surface texture analyis of Al:ZnO thin films. - We prepared thin films by means of (RF) sputtering method on the quartz substrates. - We used scanning electron microscopy, atomic force microscopy and fractal geometry. - We determined the Areal Autocorrelation Function (AACF) and pseudo-topothesy K.

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- We determined the functional, statistical and fractal surface properties of samples.