8/19/2019 PosterEMRS_2009 HRTEM3

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E.E. VasileVasileaa)), I., I. IordacheIordachebb)) and R.and R. PlugaruPlugarucc))

a)a)S.CS.C. METAV. METAV--Research & DevelopmentResearch & Development S.A,S.A, C.A.RosettiC.A.Rosetti Str Str . 31, 020011,. 31, 020011, BucurestiBucuresti

b)b)NationalNational Research and Development Institute for Electrical EngineeringResearch and Development Institute for Electrical Engineering-- ICPEICPE--CA, 313CA, 313 SplaiulSplaiul UniriiUnirii, Bucharest 030138, Romania, Bucharest 030138, Romania

c)c)NationalNational Institute for R&D inInstitute for R&D in MicrotechnologyMicrotechnology--IMT Bucharest, POIMT Bucharest, PO--BOX 38BOX 38--160, 023573 Bucharest, Romania,160, 023573 Bucharest, Romania,

EE--mail:mail: rodica.plugaru@imt.rorodica.plugaru@imt.ro

ZnOZnO films deposited by DC magnetron sputteringfilms deposited by DC magnetron sputtering

from Zn targetfrom Zn target

HRTEM study ofHRTEM study of ZnOZnO thin films deposited by magnetronthin films deposited by magnetron

sputteringsputtering

OverwievOverwiev

Recent developments in the field ofRecent developments in the field of ZnOZnO thin films for optoelectronicthin films for optoelectronic

devices have been focused on the optimization of the film structdevices have been focused on the optimization of the film structureure

since it was found that particularly (002)since it was found that particularly (002)--orientedoriented ZnOZnO films exhibitfilms exhibit

highly enhanced optical and photoluminescence properties.highly enhanced optical and photoluminescence properties.

In this paper we report the results of our investigation on theIn this paper we report the results of our investigation on the structurestructure

ofof ZnOZnO thin films deposited on glass substrates by using DC and RFthin films deposited on glass substrates by using DC and RF

magnetron sputtering.magnetron sputtering.

ExperimentalExperimental

▪▪ Zinc oxide thin films were prepared by DC and RF magnetronZinc oxide thin films were prepared by DC and RF magnetron

sputtering technique. Metallic Zn (Aldrich, 99.99%) was used assputtering technique. Metallic Zn (Aldrich, 99.99%) was used as

target in DC magnetron sputtering process.target in DC magnetron sputtering process. ZnOZnO target used in RFtarget used in RF

magnetron sputtering deposition process was obtained frommagnetron sputtering deposition process was obtained from ZnOZnO

powder (powder (UmicoreUmicore Zinc Chemicals, 99.99%). TheZinc Chemicals, 99.99%). The ZnOZnO powder waspowder was

mecanicallymecanically milled, then pressed as a disc with the diameter ofmilled, then pressed as a disc with the diameter of

4.5 cm and thickness of 3.54.5 cm and thickness of 3.5 -- 4 mm. The target was sintered at4 mm. The target was sintered at

12001200ooC for 1 h.C for 1 h.

▪▪ The sputtering processes were carried out inThe sputtering processes were carried out in Ar Ar atmosphere. Theatmosphere. The

sputtering time was 1 min and the deposited film thickness wassputtering time was 1 min and the deposited film thickness was

about 120 nm. The substrate was glass in both experiments.about 120 nm. The substrate was glass in both experiments.

ZnOZnO films obtained by oxidation of metallic Zn films are referred afilms obtained by oxidation of metallic Zn films are referred ass

““films Afilms A”” andand ZnOZnO films deposited fromfilms deposited from ZnOZnO target aretarget are refferedreffered titi

asas ““films Bfilms B””..

▪▪ The surfaceThe surface mophologymophology was investigated by using awas investigated by using a QUANTAQUANTA

INSPECT F Scanning Electron Microscope (SEM) with XINSPECT F Scanning Electron Microscope (SEM) with X--ray energyray energy

dispersive spectrometer (EDAX) and andispersive spectrometer (EDAX) and an Alpha 300 SAlpha 300 S WitecWitec  alphaalpha

300S300S System with Atomic Force Microscopy (AFM).System with Atomic Force Microscopy (AFM).

The film structure was analysed by using a High ResolutionThe film structure was analysed by using a High Resolution

TransmisionTransmision Electron Microscope (HRTEM) TECNAI F30 and aElectron Microscope (HRTEM) TECNAI F30 and a

XX--ray Diffraction System (XRD)ray Diffraction System (XRD) --  SmartLabSmartLab RigakuRigaku Corporation,Corporation,

Japan.Japan.

AcknowledgmentsAcknowledgments

This work was supported by Project 11This work was supported by Project 11 -- 048/2007048/2007--2010 Financed by MECI Romania.2010 Financed by MECI Romania.

RP acknowledges with thanks the su pport received from Dr.RP acknowledges with thanks the s upport received from Dr. C.KuskoC.Kusko for AFM filmsfor AFM films

morphologymorphology characterzationcharacterzation and from M.and from M. DanilaDanila for XRD analyses.for XRD analyses.

ReferencesReferences[1] W.[1] W. GaoGao, Z. Li,, Z. Li, ZnOZnO thin films produced by magnetron sp uttering, Ceramicsthin films produced by magnetron sputtering, Ceramics InternatInternat..

30, 115530, 1155--1159 (2004).1159 (2004).

[2] M.[2] M. SucheaSuchea, S., S. ChristoulakisChristoulakis, K., K. MoschovisMoschovis, N., N. KatsarakisKatsarakis, G., G. KiriakidisKiriakidis,, ZnOZnO

transparent thin films for gas sensor applications, Thin Solid Ftransparent thin films for gas sensor applications, Thin Solid Films 515, 551 (2006).ilms 515, 551 (2006).

[3] Y. Sato, T. Yamamoto, Y.[3] Y. Sato, T. Yamamoto, Y. IkuharaIkuhara, Atomic Structures and Electrical properties of, Atomic Structures and Electrical properties of

ZnOZnO Grain Boundaries, J. Am.Grain Boundaries, J. Am. CeramCeram. Soc. 90(2), 337 (2007).. Soc. 90(2), 337 (2007).

[4] B. Wang, J. Min, Y. Zhao, W. Sang, C. Wang, The grain bounda[4] B. Wang, J. Min, Y. Zhao, W. Sang, C. Wang, The grain boundary related pry related p--typetype

conductivity inconductivity in ZnOZnO films prepared by ultrasonic sprayfilms prepared by ultrasonic spray pyrolysispyrolysis,, ApplAppl. Phys.. Phys. LettLett. 94,. 94,

192101 (2009).192101 (2009).

[5] J.M. Yuk, J.Y. Lee, Y.S. No, T.W. Kim, W.K.[5] J.M. Yuk, J.Y. Lee, Y.S. No, T.W. Kim, W.K. ChoiChoi, Evolution mechanisms of the, Evolution mechanisms of the

surface morphology of grains insurface morphology of grains in ZnOZnO thin films grown onthin films grown on pp--InPInP substrates due tosubstrates due to

thermal annealing,thermal annealing, ApplAppl. Phys.. Phys. LettLett. 93, 021904 (2008).. 93, 021904 (2008).

EMRS 2009 Strasbourg FranceEMRS 2009 Strasbourg France

Density distr.

0.00000

1.00000

2.00000

3.00000

4.00000

5.00000

6.00000

0.000 50.000 100.000

Density Distr.

Depth(nm)

   D  e  n  s   i   t  y   (  g   /  c  m   3   )

Meas.data

Simulation

10 -7

10 -6

10 -5

10 -4

10 -3

10 -2

10 -1

100

0.0000 5.0000 10.0000

REFLECTIVITYPROFILE

2theta angle (deg.)

   R  e   f   l  e  c   t   i  v   i   t  y   (  a .  u .   )

 No. Layer Thickness Density Roughness Period

Func.

(nm) (g/cm3) (nm)

- -- -- - -- -- -- -- - - -- -- -- -- -- - - -- -- -- -- -- -- - - -- -- -- -- -- - - -- -- -- ---

2 ZnO 1.63(2) 1.55435[--] 0.422(5) Linear 

1 ZnO 89. 9(19) 1 .32(4) 3 .0 (2 ) L inea r  

0 GLASS 0.000[--] 2.21000[--] 4(3) Const.

ZnOZnO films deposited by RF magnetron sputteringfilms deposited by RF magnetron sputtering

fromfrom ZnOZnO targettarget

 

0.0e+000

  1.0e+003

  2.0e+003

  3.0e+003

  4.0e+003

  5.0e+003

   Z  n   O ,   (

   1   0   0   )

   Z  n   O ,

   (   0   0   2   )

   Z  n   O ,   (

   1   0   1   )

   Z  n   O ,

   (   1   0   2   )

   Z  n   O ,   (

   1   1   0   )

   Z  n   O ,   (

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   Z  n   O ,

   (   2   0   0   )

   Z  n   O ,   (

   1   1   2   )

   Z  n   O ,

   (   2   0   1   )

20 30 40 50 60 700.0e+000

  2.0e+003

  4.0e+003

  6.0e+003

  8.0e+003

  1.0e+004

   I  n   t  e  g  r  a   t  e   d   I  n   t  e  n  s   i   t  y   (  c  p  s   d  e  g   )

2-theta(deg)

Meas. data:Zn!Q/Data 1Zn O

   I  n   t  e  n  s   i   t  y   (  c  p  s   )

Zn O

Meas. data

Simulation

10 -8

10 -7

10 -6

10 -5

10 -4

10 -3

10 -2

10 -1

100

0.0000 5.0000 10.0000

REFLECTIVITYPROFILE

2theta angle(deg.)

   R  e   f   l  e  c   t   i  v   i   t  y   (  a .  u .   )

Densitydistr.

0.00000

1.00000

2.00000

3.00000

4.00000

5.00000

6.00000

0.000 50.000 100.000 150.000

Density Distr.

Depth(nm)

   D  e  n  s   i   t  y   (  g   /  c  m   3   )

 No. Layer Thickness Density Roughness Period Func.

(nm) (g/cm3) (nm)- -- - -- -- -- -- -- -- - - -- -- -- -- -- -- - - -- -- -- -- -- - - -- -- - - -- -- -- -- -- --

2 Z nO 1.244(14) 1 .03385[- -] 2 .79(6) Li ne ar  

1 ZnO 102.0(2) 1.17(2) 1.41(3) Linear 

0 GLASS 0.000[--] 2.21000[--] 0.0(16) Const.

ConclusionsConclusions

 

SEM images of films "A" show grains of ~ 100 nm in average sizeSEM images of films "A" show grains of ~ 100 nm in average size,,

with columnar structure and a relative large porosity.with columnar structure and a relative large porosity.

Films "B" present smooth surfaces with spherical grains of ~ 35Films "B" present smooth surfaces with spherical grains of ~ 35

nm innm in

average size.average size.

The characteristics of the films morphology, structure andThe characteristics of the films morphology, structure and optoopto--

electrical properties related to the two method of deposition weelectrical properties related to the two method of deposition we rere

previously reported [1,2].previously reported [1,2].

▪▪ HRTEM images of films "A" showHRTEM images of films "A" show nanocrystallinenanocrystalline regions of ~10regions of ~10--1515

nm in size. Thenm in size. The nanocrystallinenanocrystalline domains have different orientationsdomains have different orientations

and are separated by well defined grain boundaries.and are separated by well defined grain boundaries.

Various [0001] tilted grain boundaries may be observed, as prevVarious [0001] tilted grain boundaries may be observed, as previouslyiously

revealed inrevealed in ZnOZnO bicrystalsbicrystals [3].[3].

HRTEM images of the films "B" show small crystalline volumes.HRTEM images of the films "B" show small crystalline volumes.

NanocrystallineNanocrystalline domains are surrounded by large and stronglydomains are surrounded by large and strongly

defective grain boundaries.defective grain boundaries.

▪▪ EDAX spectra evidence a reducedEDAX spectra evidence a reduced IIZnZn /I /IOO ratio in films "A" oxidized inratio in films "A" oxidized in

air at 450air at 450ooC for 3h, that indicates an increased oxygen contentC for 3h, that indicates an increased oxygen content

comparatively with the ascomparatively with the as--depositeddeposited ZnOZnO films (films "B").films (films "B").

The dependence of theThe dependence of the crystallinitycrystallinity on the oxygen content wason the oxygen content was

previously reported [4]; it has a strong influence on the structpreviously reported [4]; it has a strong influence on the struct ure ofure of

the grain boundaries and electrical properties.the grain boundaries and electrical properties.

▪▪ 2D and 3D AFM images and topography profiles reveal that regions2D and 3D AFM images and topography profiles reveal that regions

of columnar grains with an abnormal size a re randomly distributeof columnar grains with an abnormal size are randomly distributed ond on

the surface of films "A".the surface of films "A".

Grains with more uniform size distribution are present in filmsGrains with more uniform size distribution are present in films "B". A"B". A

mechanism for the grain growth inmechanism for the grain growth in ZnOZnO films was proposed andfilms was proposed and

related with the surface morphology [5].related with the surface morphology [5].

▪▪ The XRD pattern of film "A" reveals their polycrystalline strucThe XRD pattern of film "A" reveals their polycrystalline structureture

with (100), (002) and (101) orientedwith (100), (002) and (101) oriented nanocrystallsnanocrystalls. The. The nanocrystallsnanocrystalls

size is ~ 10.5 nm.size is ~ 10.5 nm.

The XRD pattern of asThe XRD pattern of as--deposited film "B" shows that the film has adeposited film "B" shows that the film has a

poorpoor crystallinitycrystallinity, with (002) preferential orientation. The, with (002) preferential orientation. The nanocrystallsnanocrystalls

size is ~ 11.7 nm.size is ~ 11.7 nm.

▪▪ The reflectivity profiles reveal the increased porosity and surf The reflectivity profiles reveal the increased porosity and surf aceace

roughness of films "A" comparatively with the asroughness of films "A" comparatively with the as--depositeddeposited ZnOZnO filmsfilms

"B"."B".

SEM images of ZnOfilm deposited from Zn metallic target and oxidized in air at 450oC, 3h (a,b). The film thickessin the

SEM cross section image is 92.5 nm (c).

HRTEM images of crystalline grains in ZnOfilmdeposited from Zn metallic target (a). Magnified

HRTEM image of grains surrounded bydefective region of grain boundaries (b, c, d).The ratio IZn /IO intensity in EDAX spectrum is3.4 (e)

AFM 2D (a) and 3D images (b) of a ZnO film obtainedfrom Zn metallic target, showing areas of large grains

randomly distributed on the surface, as well as smallgrains. Vertical (c) and horizontal (d) profiles.T he

grains height is in the range: 30-140 nm.

X-ray diffraction: pattern

(a), Reflectivity profile (b),Density distribution (c) of

ZnO film depostedfrom Zn

metallic target.

 AFM:

SEM images of the as deposited ZnO film surface (a). Relative uniform grains size about 22-35 nm(b).

HRTEM, EDX

 0.0e+000

  1.0e+003

  2.0e+003

  3.0e+003

  4.0e+003

  5.0e+003

   Z  n   O ,   (

   1   0   0   )

   Z  n   O ,   (

   0   0   2   )

   Z  n   O ,   (

   1   0   1   )

   Z  n   O ,   (

   1   0   2   )

   Z  n   O ,   (

   1   1   0   )

   Z  n   O ,   (

   1   0   3   )

   Z  n   O ,   (

   2   0   0   )

   Z  n   O ,   (

   1   1   2   )

   Z  n   O ,   (

   2   0   1   )

20 30 40 50 60 70  0

  10

  20

  30

  40

  50  60  70  80  90  100

Zn O

2-theta(deg)

Meas.data:Zn!Q/Data1ZnO

   I  n   t  e  n  s   i   t  y   (  c  p  s   )

(a) (b)

(c)

(d)

AFM 2D (a) and 3D images (b) of an as deposited ZnO

film, showing grains with relatively uniform size allover the surface. Vertical (c) and horizontal (d) profiles.

The grains height is i n the range: 80-120 nm.

(a) (b)

(c)

(d)

(a)

(c)

(b)

(a)

(d)

(a)

(d)(c)

(a) (b)

(a)

(b)

(c)

X-ray diffraction: pattern(a), Reflectivity profile (b),

Density distribution (c) ofZnOfilm depostedfrom

ZnOtarget.

(a)

(b)

(c)

HRTEM images of crystalline grains in as

deposited ZnO film (a). Magnified HRTEM imageof crystalline grains surrounded by defectiveregions. Crystalline order on the smal volumes(b, c, d). The ratio IZn /IO intensity in EDAXspectrum is 3.7 (e).

(a) (b)

(c)

(b)(a)