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Journal of Sol-Gel Science andTechnology ISSN 0928-0707 J Sol-Gel Sci TechnolDOI 10.1007/s10971-014-3281-0

SAXS and WAXS analysis of MgO dopedZnO nanostructured ceramics grown on Siand glass substrate

Ilghar Orujalipoor, Arda Aytimur,Caner Tükel, Semra İde & İbrahim Uslu

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ORIGINAL PAPER

SAXS and WAXS analysis of MgO doped ZnO nanostructuredceramics grown on Si and glass substrate

Ilghar Orujalipoor • Arda Aytimur •

Caner Tukel • Semra Ide • Ibrahim Uslu

Received: 17 July 2013 / Accepted: 18 January 2014

� Springer Science+Business Media New York 2014

Abstract The study performs preparation of the precur-

sor thin films with MgO doped ZnO nanocrystalline

ceramics by electrospinning technique and their charac-

terizations by small and wide angle X-ray scattering

methods. The prepared films on Si and commercial glass

wafers as nanoceramic mats were calcined at 320, 340, 360

and 380 �C. The role of the annealing conditions on the

morphological changes and uniformity of the films was

also investigated. Results show that, the thermal process

and choice of the wafer are critical for film morphology at

the nano and atomic scales through the network shrinkage

and crystallization, respectively. Samples show mono/poly

disperse isolated nanoclusters/regular lamellar distribu-

tions/and embedded aggregations.

Keywords Electrospinning � Nanostructured ceramics �SAXS � WAXS

1 Introduction

In recent years, a lot of researchers have focused on prep-

aration and characterization of new nanostructured ZnO

thin films to reach many interesting physical properties

which are necessary in industrial and technological appli-

cations for optic, electric and magnetic devices. The men-

tioned interesting physical properties can be used for

nanoscale electro-mechanical fabrication. These type sam-

ples are highly-symmetric and they can cause crystalline

nano needle, rod, belt, ring, helix, combs, etc. aggregates.

Hexagonal (wurtzite) structure of ZnO helps lattice-

matching and controlled growth. Positive Zn surfaces and

negative O surfaces create electric dipoles that facilitate

polarization growth along certain directions and planes

under applied voltage and temperature. So, different prop-

erties of new prepared zinc oxide can be defined, controlled,

improved and used in technological developments.

Zinc oxide structures have large exciton binding energy

(i.e. 60 meV) and band gap energy (3.37 eV at room

temperature) with a variety of applications including cat-

alysts, gas sensors, thin film-based electronic and electro-

optic devices, and varistors [1–5].

Small amount of dopant metal oxide materials such as

MgO, Bi2O3, Co3O4, MnO, Sb2O3, Cr2O3 and etc. are the

main tools to produce higher band gap ZnO alloys for

possible quantum well structures [6, 7].

In this study, MgO has been chosen for a dopant because

a large number of reports indicate the enhancement of band

gap of ZnO by doping it with different concentrations of

MgO [8].

Electrospinning technique has been used to prepare

these type doped films because of its simple applications

and the low cost. The synthesis of Mg doped zinc oxide

nano particles has been carried out by electrospinning

I. Orujalipoor � C. Tukel

Department of Nanotechnology and Nanomedicine, Hacettepe

University, Beytepe, Ankara 06800, Turkey

A. Aytimur

Department of Advanced Technologies, Gazi University,

Besevler, Ankara 06500, Turkey

S. Ide (&)

Department of Physics Engineering, Hacettepe University,

Beytepe, Ankara 06800, Turkey

e-mail: side@hacettepe.edu.tr

I. Uslu

Department of Chemistry Education, Gazi University,

Besevler, Ankara 06500, Turkey

123

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DOI 10.1007/s10971-014-3281-0

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process using 10 % poly(vinyl alcohol) (PVA) as polymer

solution, zinc acetate and magnesium acetate as reagents.

Metal acetates such as zinc acetate and magnesium ace-

tates, are useful reagents in organic synthesis of metal

oxide nano structures [9].

Shape, size and distributions of ZnO nanoaggregations

and its morphology dependent properties are also taking

much interest in nanoscience and technological applica-

tions [10].

The dielectric behaviors and charge carrier transport of

MnO doped ZnO films including nanostructured aggrega-

tions may be improved due to high surface area per unit

volume, small particle size and quantum confinement of

charges [11, 12].

Cubic structure of MgO can be easily replace in matrix

of hexagonal ZnO crystal structure because of quite similar

materials. MgO doped ZnO films with high dielectric

constant may be also used in capacitor applications as thin

dielectric layers to improve storage capability of a capac-

itor [12].

These type structural information related with their

nanosized aggregates can be obtained by several comple-

mentary experimental methods such as small angle X-ray

scattering (SAXS), SANS, XRD, HRTEM, STEM, EDX

and XPS methods [10, 13].

The main purpose of the work may be summarized as

investigation of the nanostructured aggregations, surface

morphologies, annealing and substrate effects, and under-

standing of functional properties on structure and mor-

phology with the other near future planned studies.

In the present work (as a part of our ongoing resear-

ches), two group (with Si and glass substrate) MgO doped

ZnO nanocrystalline ceramic films have been prepared and

they have been annealed at 320, 340, 360 and 380 �C. The

prepared eight samples have been investigated by SAXS

and wide angle X-ray scattering (WAXS) analysis to

investigate different substrate and annealing temperatures.

2 Experimental procedure

The experimental procedure of the sample preparation

consists of three major steps previously applied by us [9] as

seen in Fig. 1. PVA powder (had average Mw

85,000–124,000 g/mol) was obtained from Sigma Aldrich;

zinc acetate and magnesium acetate were obtained from

Merck. Ultrapure deionized water was used as a solvent.

Aqueous PVA solution (10 %) was first prepared by

dissolving the PVA powder in ultra pure distilled water and

heating it at 80 �C, stirring it for 3 h and then cooling it to

room temperature while continuously stirring it for 2 more

hours. In the experiments, four hybrid polymer solutions

were prepared. A typical procedure; 2 g of zinc acetate and

0.04 g of magnesium acetate were added into a 40 g

aqueous PVA at 60 �C separately and drop by drop, and the

solution was vigorously stirred for 3 h at this temperature

for the reaction to occur between the PVA and the metal

acetates. Stirring was continued for another 3 h at the room

temperature. Thus, viscous gels of the PVA/Zn–Mg acetate

hybrid polymer solutions were obtained.

The hybrid polymer solutions were poured in syringes,

the needle (18 gauge) being connected to the positive ter-

minal of a high-voltage supply (Gamma High Voltage

Research) which was able to generate DC voltages up to

40 kV. The suspension was delivered to the needle by a

syringe pump (New Era Pump Systems Inc., USA). The

distance between the tip of the needle and the aluminum

collector was fixed at 21 cm. The following operative

parameters were chosen: a flow rate of 0.4 ml/h and an

applied voltage of 25 kV. Si wafers and glass slides were

pasted to the aluminum collector in order to coat them via

electrospinning. Thus the Si wafers and glass slides were

coated with magnesium oxide doped (ZnO) nanofibers. The

fibers formed as a result were dried in vacuum for 12 h at

80 �C.

The one part of Si wafers containing nanofibers was

calcined a rate of 5 �C/min and remained 1 h at 4 different

temperatures namely 320, 340, 360 and 380 �C at atmo-

spheric conditions to obtain magnesium oxide doped zinc

Fig. 1 Major steps of the sample preparation

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oxide nanofibers. Similar process was also followed for

glass substrate.

In order to investigate the molecular and nanometer

scaled structures, MgO doped ZnO films have been char-

acterized by using SAXS and WAXS methods. Combined

SAXS and WAXS measurements are very useful tools to

obtain the hierarchical structural information from the

packing of crystallographic structure to bigger nanosized

stacking [14].

A micro-line collimation Hecus SWAXS System3 has

been used with conventional X-ray source (CuKa) and

ISO-DEBYEFLEX 3003 generator (50 kV–50 mA) during

the scattering measurements at 23 �C and in 700 s as

measuring time. Small and wide angle scattering data have

been recorded in q (magnitude of the scattering vector)

ranges of 0.004–0.5 A-1 and 2h (scattering angle) of 18�–

26�, respectively. There is a correlation between magnitude

of scattering vector, scattering angle and wave length (k) of

the used X-rays in the form of q = (4p/k)sinh. The mea-

sured SAXS and WAXS profiles of the samples were given

in Figs. 2, 3 and 4.

3 Results and discussion

3.1 SAXS analysis

Structural information about nanostructured content and their

distance distributions, maximum grain size, homogeneity of

the samples and the surface morphologies can be obtained by

this analysis [15]. The nanostructured formations and crys-

talline structures were obtained with SAXS and WAXS

analysis for the studied type films is illustrated in Fig. 5.

Nanostructured content gives an evidence related the

presences of globular (3D), flat (2D) and rod shape (1D)

nanoaggregations in these type samples. The effective sizes

(Rg) and shapes of the aggregations (globular, flat and rod)

can be determined in Guinier region (q ? 0) of the SAXS

data by the following equations under the limit of qRg B 1.

[16]. SAXS results in Guinier approximation represent

statistical average related with size and shape of the nano

fractals (Table 1).

Globular; IðqÞ ¼ Ið0Þ exp �q2R2

g

3

" #ð1Þ

Flat; IðqÞ � q2 ¼ Ið0Þ exp �q2R2

g

2

" #ð2Þ

Rod; IðqÞ � q ¼ Ið0Þ exp �q2R2

g

2

" #ð3Þ

Fundamental SAXS results related with Guinier Region

showed that the increase in the calcination temperature

implies different size and forms of the nano aggregations,

as expected. More detailed analyses have been started after

the evidence of these related nano size aggregations. These

size and shape information are including a useful structural

information to well started refinements of the all data.

Fig. 2 SAXS profile (graphic of Log I-Log q) for the films with Si

Fig. 3 SAXS profile (graphic of Log I-Log q) for the films with

Glass (Color figure online)

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Fig. 4 WAXS profile for the

films with Si

Fig. 5 Structural definitions

about a thin film: a A monolayer

film morphology along the

normal of the film, b a

conventional surface

morphology perpendicular to

the surface and c its nanosize

aggregations including different

electron densities and

crystalline regions

Table 1 Shapes and effective

sizes (nm) of the obtained

nanoaggregations

Temp. (�C) Silicon Glass

Globular Flat Rod Globular Flat Rod

320 – – 12.8 ± 0.9 22.9 ± 0.5 7.3 ± 0.9 17.4 ± 0.4

340 – – 8.7 ± 1.1 23.0 ± 0.4 5.1 ± 1.0 16.1 ± 0.5

360 – 12.5 ± 0.9 – – 14.6 ± 0.6 –

380 – 12.7 ± 0.8 13.9 ± 0.6 – 15.2 ± 0.5 –

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Surface morphologies of the films were also investigated

by the calculation of fractal dimensions (p). An approxi-

mation about big q range (q ? ?) defined by Porod region

of SAXS profile indicates a proportionality of I(q) * q-p

[15, 16]. Structural information about the surfaces can be

determined according to the value of p. A combined

function (defined in the software of IGOR program [17])

Table 2 Surface morphologies

(fractal dimensions) determined

by Porod approximation

Temp. (�C) Silicon Glass

320 3.00 2.53

340 2.89 2.21

360 2.85 2.50

380 2.85 2.61

Fig. 6 PDDF and Moore’s indirect inverse Fourier transformation fitting results [18] (Color figure online)

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including rod, flat and globular form factors was formed

and used for fitting process to reach p information. The

condition of 0 \ p \ 3 indicates mass fractals while the

means of 3 \ p \ 4 is surface fractals and 4 B p gives the

evidence of smooth surface scatterers. The calculated

fractal dimensions of the samples showed the formation of

mass fractals in the surfaces as seen in Table 2.

The distance distributions, maximum grain size and

homogeneity of the samples have been also investigated by

creation of pair distance distributions functions (PDDF)

related with the samples. These visualizations of Fig. 3

provide a better understanding of these analyses and have

different groups (columns for Si and glass) and eight graphics

for different thermal application as seen. Each graphic firstly

has scattering data and fitting result (left vertical and down

horizontal axes) with blue and green colors and secondary

has PDDF and distance (right vertical and up horizontal) with

histogram representation. With the help of these distribu-

tions, some grains and lamellar type stackings of MgO doped

ZnO nanocrystalline ceramic materials in the surface of the

substrate may be obtained easily and homogeneity of the

films can be controlled. Uniform distributions can be detec-

ted with a big unique hump such as determined in 360-glass

sample. 340-Si sample has six main type discrete grains

(indicated by discrete blue lines and stacking of histograms)

with the maximum size range of 8.7–18.0 nm as seen in

Fig. 6. This sample is far from a homogeneous surface, but

may be useful to create nano sized holes in the surface with

different annealing process.

320-Si is a good sample for the mentioned uniform

nanosize clusters in the film structure. Maximum grain size

is around 3.7 nm (related with small humps in small q

range of the distribution) and the center to center distances

between these small grains is approximately equal to

5.2 nm. Lamellar stacking can be also followed by a peak

observed in scattering data (green color) of Si-340, 360 and

380 and these lamellar distance is deviating from big q

range to the small q range with increasing temperature as

expected and intensity of the peak is also decreasing during

the annealing as expected. These structural formations can

be simulate and describe by a previously observed AFM

view given in Fig. 7.

360-Glass and 380-glass samples has homogeneity in a

big islands with a maximum size 150 and 151 nm with

nanoaggregations size of 59.4 and 59.5 nm and the most

possible distance between these nanoaggregations of

76.0 nm. It may be said that, in these temperatures of

annealing, nanoaggregations are starting to embedding into

glass.

More detailed peak analysis and thermal effect can be

seen in Figs. 2 and 3 by using main scattering data. SAXS

profiles for three samples (2-340, 360, 380) show that su-

perlattice peaks seen in the logarithmic scale I(q) - q

graphics are sliding through to the smaller q range with

increasing annealing temperatures. The obtained period

lengths for these peaks are increasing (1.1, 1.6 and 2.0 nm,

respectively) as expected. The superlattice structure dem-

onstrates a high layer quality with well-defined chemical/

physical modulations. Increasing temperature is causing

bigger inter planar distances (smaller q values of the peaks,

d = 2p/q) and lower intensities which mean the embedded

ceramic aggregations into substrate.

The scattering effect of the well distributed nanoaggre-

gations in the structure of 360 and 380-glass samples can

be also seen in the logarithmic graphics of SAXS data

given by Fig. 3. Dark and light blue colored data have

recordable humps around d = 3.6, 1.4 and peaks around

1.1 nm. These values are indicating the possible distances

or correlation lengths between nanoaggregations. The

structure has clusters including the smaller nanoaggrega-

tions with approximate size of 15 nm (Table 1).

3.2 WAXS analysis

Atomic layers related with crystal structures of ZnO, MgO

and Si substrate may be also detected by WAXS mea-

surements. The appeared peaks in WAXS diagrams of 340,

360, 380-Si samples have been investigated by using the

known crystallographic information of Si; Fd3m, cubic,

a = 5.43 A: ZnO; P63 mc, hexagonal, a = b = 3.35

c = 5.22 A and MgO; Fm3m, cubic, a = 4.216 A [19–21].

The displayed broad peak groups have been recorded

around d = 3.80, 4.68 and 5.25 A for 340, 360 and 380-Si

samples, respectively in WAXS data as seen in Fig. 4.

These peaks may not be indexed because of poor resolution

of data and possible multiple crystallographic diffraction

effects, but they are also indicative for ZnO crystallization

Fig. 7 A simulation of the surface morphologies by using an AFM

view

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and characteristic for the films. Crystallization takes place

at 340 �C in the structural content of big grains and clusters

and then, increased annealing temperature cause to distri-

bution and spreading of big clusters to the surface of the

film. So, the weaker lamellar electronic density contrast

started to exist in ceramic matrix.

The related SAXS–WAXS data and more detailed

structural information may be obtained from the authors.

4 Conclusions

The in situ growth of nanostructures has been investigated

by SAXS and WAXS methods and the results have high

potential for our future applications to produce nano layer

type holes and clusters in the surface of the films.

SAXS and WAXS analysis has revealed some useful

structural information about surface morphologies and cre-

ation of nano size aggregations in the novel prepared cera-

mic thin films such as mentioned in the several previous

studies [22, 23], too. The performed analyses show that;

• Si is more convenient as substrate to create periodic

lamellar and big size nanoformations in the surface of

the films. The samples with Si consist of isolated

nanoclusters regularly planar distributed in the crystal-

line Si matrix. In these samples, the nano-ordered

disperse domain formation is starting from atomic

fractals (at 320 �C) and passing through to the occur-

ring of big clusters (grains at 340 �C), lamellar order of

big clusters, disorder of lamellar ordering at 360 �C and

finally homogenous surface morphologies at 380 �C.

• All of the samples have mass fractals indicating atomic

monomers as expected in the surface and in the region

between substrate and ceramic coating. Determination

of the mass fractals may be also given as evidence of

high surface area per unit volume, small size of

nanoaggregations and quantum confinement of charges

which cause to the expected dielectric behaviors [11,

12].

• The high uniformity of the deposited films are obtained

for 360, 380-glass samples big probably because of

amorphous glass matrix which may cause homoge-

nously embedding of ceramic nanoaggregations.

• The surface of 320, 340-glass and 340, 360-Si are not

smooth as obtained in the pair distance distributions of

the mentioned samples.

• Surface morphologies and nanostructured formations

are effected by Si and glass substrates and annealing

temperatures of the samples.

• The MgO dopants play an important role in the primary

growth stage, resulting in initial growth seeds having

diverse crystallographic structures, which are critical

for the generation of doped nanocrystals with different

shapes.

Acknowledgments TUBITAK is gratefully acknowledged for the

financial support on TBAG 111T001 project.

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