Optical properties of La2O3doped diamond-like carbonfilms
Zhenyu Zhang*,Fengwei Huo*,Zhenyuan Jia,Dongming Guo,Zhuji Jin,Renke Kang
Key Laboratory for Precision and Non-Traditional Machining Technology of Ministry of Education,Dali
an University of Technology,Dalian116024,People’s Republic of China
1.Introduction
Diamond-like carbon(DLC)films have attracted much atten-
tion for their important applications in thefields of optics,solid-
state devices,etc.,due to their exceptional properties,such as low
infrared absorption,transparency to visible light,and chemical
inertness[1,2].As DLCfilms have adjustable wide band gaps and
refractive indices,they can be utilized as protective coatings for
infrared windows and as anti-reflective coatings for solar cells
[3,4].Hydrogenated DLCfilms with the variation of hydrogen
content can control the optical band gaps,which can increa the
efficiency of solar cells[2].Nitrogen incorporated DLCfilms
deposited by puld unfiltered cathodic vacuum arc increa the
intensity of photoluminescence,compared with pure DLCfilms
[5,6].The double layer structure of the diamond-like carbon/
porous silicon(PS)can increa the intensity of photolumines-
cence(PL),which makes DLCfilms be suitable for the application
of solar cells[7].While,the poor stability in time of the PS
transforms from PS into SiO2,indicating the failure of this
structure.Also,the single element of hydrogen and nitrogen
电竞女神
doped DLCfilms also face the instable shortcomings with the time
going on,such as the oxidation and penetration to the surface,
then entering into the air.
On the other hand,the doping of La2O3into TeO2glass results in
the decrea of optical energy gap,and the increa of the width of
the localized states[8].La2O3bad glass with various visible
emissions are uful for developing new color light sources,
fluorescent display devices,UV-nsor and tunable visible lars
[9].Furthermore,La2O3bad glass has been considered as a ideal
material for broadband opticalfiber amplifier[10].As La2O3films
are photoactive,it has been ud as a photoelectrode[11].
Moreover,La2O3as dopant has exhibited excellent tribological
手抄报全国一等奖[12,13]and mechanical properties[14,15],so it can be doped in
optical protective coatings enduring the mechanical and tribolo-
gical environments.
Various physical and chemical methods have been employed to
synthesize DLCfilms,such as ion deposition,ion assisted
sputtering,sputtering,cathodic vacuum arc,plasma deposition,
puld lar deposition[16].Among the methods,cathodic
vacuum arc and puld lar deposition have the high deposition
efficiency,while it will produce surface with nonuniform thickness
曼谷旅游景点
and bigger particles on the surface.Moreover,ion deposition,ion
assisted sputtering,and plasma deposition methods usually equip
骂人语言
the expensive ion/plasma generating devices,and are difficult to go
on multi-target deposition and accurately control the concentra-
tion of different elements.Unbalanced magnetron sputtering
(UMS)is widely ud for the synthesis of DLC thinfilms,and it can
accurately control the element concentration during the multi-
target deposition.UMS allows the simple and relatively inexpen-
sive low-temperature over a large area and allows for the uniform
coating of substrates having different shapes and sizes[17,18].
To dissolve the instability of single element within the DLC
amorphous matrix with the time elapsing,a novel stable
compound of La2O3doped DLCfilms have been deposited by个人年度考核总结
unbalanced magnetron sputtering(UMS).The optical properties
are measured and analyzed.
Applied Surface Science254(2008)7193–7197
A R T I C L E I N F O
Article history:
Received17December2007
Received in revid form9May2008
Accepted14May2008
Available online20May2008
Keywords:
La2O3
DLC
Photoluminescence
Unbalanced magnetron sputtering
A B S T R A C T
A novel kind of La2O3doped diamond-like carbon(DLC)films with thickness of100–120nm were
deposited by unbalanced magnetron sputtering.Raman spectra and photoluminescence properties were
measured by Raman spectrometer operated by325nm He-Cd lar and514nm Ar+lar,respectively.
游客照The intensities of Raman spectra and photoluminescence are higher than tho of pure DLCfilms.The
La2O3doped DLCfilms have the potential promising for the application of solar cell coatings.
ß2008Elvier B.V.All rights rerved.
*Corresponding authors.Tel.:+8641184709794;fax:+8641184709794.
E-mail address:zzy@(Z.Zhang),(F.Huo).
Contents lists available at ScienceDirect
Applied Surface Science
journal homepage:/locate/apsusc
0169-4332/$–e front matterß2008Elvier B.V.All rights rerved.
doi:10.1016/j.apsusc.2008.05.267
2.Experimental details 2.1.Deposition parameters
The La 2O 3doped DLC films were deposited by UMS on Si (100)substrates using a pair of La and C targets with dimensions of 435mm Â94mm Â8mm and purity of 99.99%,respectively,as deposition source.The Si (100)substrates were supersonically cleaned in acetone solution for 10min before fixing on the substrate holder rotating around the targets to deposit uniformly.Prior to deposition,the chamber was first evacuated down to 6Â10À3Pa,and purged with Ar veral times.Then,samples were sputter cleaned for 10min using Ar +at a pressure of 6Pa and À700V bias voltages.Deposition
of La 2O 3doped DLC films was performed by magnetron sputtering controlled by mid-frequency power (40kHz)with Ar and O 2in a ratio of 11:1at a chamber pressure of 3.1Â10À1Pa for 10min.After the deposition,the substrate was cooled inside the chamber in an Ar atmosphere.The La 2O 3concentration within the DLC films was controlled by the power ratio applied on the La and C targets,respectively.Under the same parameters,DLC and 1,2,3,4,5,6,7,8,12,14%La 2O 3doped DLC films were deposited.2.2.Measuring methods
The surface morphology was measured by Sieko SPA-300HV atomic force microscope (AFM,Sieko SPA-300HV,Japan).La 2O 3atomic bonding state was obtained by X-ray photoelectron spectrometer (XPS,ULVAC-PHI Quantera,Japan).PL and Raman measurements were both performed by Raman spectrometer operated with 514nm Ar +lar and 325nm He-Cd lar (Renishaw 1000,UK),respectively.Film thickness was measured by spectro-scopic ellipsometer (Sopra GES-5,France).3.Results and discussion 3.1.XPS spectra
Fig.1shows the XPS spectra of 6%La 2O 3doped DLC film.La3d signals consist of the 3d 3/2and 3d 5/2spin-orbit doublets (Fig.1(a)).La3d peaks are centered at 834.7and 851.4eV.Shape and binding energy values for prent La features agree well with the standard La 2O 3XPS spectra data [19,20].The deconvoluted C1s spectrum exhibits three peaks at binding energies of 284.4,286.5,288.
班主任心得体会1eV
(Fig.1(b)).The peaks correspond to sp 2,sp 3and C–O bond [21,22].According to the XPS spectra of La3d and C1s,La 2O 3is formed within the films.3.2.AFM characterization
The film thickness of DLC and all La 2O 3doped DLC films are in the range of 100–120nm.Fig.2(a)and (b)show AFM micrographs of 3and 5%La 2O 3doped DLC films,respectively.The surfaces of two films consist of uniform sphere-like particles with diameter of about 20and 25nm,and corresponding surface roughness Ra is 0.61and 0.68nm.All the surface roughness of La 2O 3doped DLC films are in the range of 0.6–0.8nm,which is higher than that of pure DLC films (0.33nm).This may be attributed to the faster deposition speed of La metal ions in the same electric field than that of C ions.As La metal atoms sputtered form the targets is easier to be ionized in the same electric intensity than that of C atoms,the ionized La atoms can obtain faster deposition speed than C ionized atoms,so the nanoparticles of La 2O 3doped DLC films can grow bigger than tho of pure DLC films.3.3.Raman spectra
Fig.3(a)shows the Raman spectra operated by 325nm He-Cd lar of DLC and ten kinds of La 2O 3doped DLC films.All the Raman spectra exhibit an asymmetric broad shape in the range of 1000–1
800cm À1,accompanying the D and G peak located at 1350and 1560cm À1,which is the obvious characteristic of DLC films [23,24].Raman spectra are characterized as a combination of two bands,typically labeled as D and G peaks and are attributed to the breathing mode of aromatic rings and in-plane bondstretching of pairs of bonded C atoms,respectively [25–27].To obtain the accurate positions of D and G peaks,the experimental curves of 6%La 2O 3doped DLC films are fitted with two Gaussian lines,as shown in Fig.2(b).With the doping of La 2O 3,the D peak shoulder is obvious,which indicates that the fraction of sp 2bonded C prent in the films is higher than that of pure DLC films.This is accompanied by an increa in ordering due to the formation of larger clusters of aromatic rings [25].To confirm the sizes of nanoparticles obtained in AFM micrographs (Fig.2),the full width half maximum (FWHM)of Raman spectra of 3and 6%La 2O 3doped DLC films are ud to evaluate the sizes of nanoparticles,the corresponding sizes of nanoparticles are approximately 23and 25
nm.
Fig.1.XPS spectra of (a)La3d and (b)C1s peaks of 6%La 2O 3doped DLC film.
Z.Zhang et al./Applied Surface Science 254(2008)7193–7197
7194
3.4.PL spectra
Fig.4(a)shows PL spectra of DLC and La 2O 3doped DLC films.To compare the intensity and shape of PL spectra,all the PL spectra are normalized on the vertical direction with the same horizontal axis.The first sharp peaks located at around 529nm are the Raman signal [28]and the cond sharp peaks situated at about 535nm of DLC and 1–2%La 2O 3doped DLC films are also the Raman signal.The third asymmetric peak located at around 559nm is the Raman G peak,and the fourth approximately symmetric broad band centered at about 607nm is the Raman 2G peak.The last approximated symmetric broad band centered at about 664nm is the PL spectra [29].With the increasing of La 2O 3concentration within DLC films,the intensity of PL spectra increas and saturates at the concentration of 2%.As the PL spectra is due to the recombination of electron hole p
意料的意思
airs within sp 2bonded clusters in an sp 3bonded amorphous matrix [28],the PL intensity increas with the doping of La 2O 3,resulted primarily from the saturation of nonradiative recombination sites (e.g.,dangling bonds).To obtain the accurate PL intensity and parate the contribution of different bands,the PL spectrum of 6%La 2O 3doped DLC film is fitted with four Gaussian functions,as shown in Fig.4(b).
3.5.Relative intensity ratio I D /I G and relative PL intensity
Fig.5(a)shows the relative intensity ratio I D /I G and G peak position as a function of La 2O 3concentration in DLC films.Also Fig.5(b)shows the relative PL intensity obtained by taking the area of the broad band during the fitting of the PL spectra (Fig.4(b))as a function of La 2O 3concentration in DLC films.G peak position of La 2O 3doped DLC films shifts to a higher wavenumbers compared with pure DLC film,which corresponds to the increa of sp 2concentration [30,31].The intensities of G peak position,relative intensity ratio I D /I G ,and relative PL intensities of La 2O 3doped DLC films are higher than tho of pure DLC films.The increa of the relative PL intensity of La 2O 3doped DLC films correlates well with the increa of G peak position and I D /I G ,indicating that the enhanced PL is a conquence of carrier localization within an increasing number of sp 2rich clusters [28].The doping of rare earth oxide La 2O 3has no direct influence on the PL and Raman sp
ectra,while it can alter the internal bonding structures of C element,such as sp 2/sp 3fraction and concentrations of C–O,sp 2and sp 3bonds,which can directly influence on the PL and Raman spectra [22].The variation of sp 2/sp 3fraction,and the concentra-tion of sp 2and sp 3concentration result in the increa of PL and Raman
spectra.
Fig.2.AFM micrographs of (a)3%and (b)6%La 2O 3doped DLC
films.
Fig.3.(a)Raman spectra of DLC and ten kinds of La 2O 3doped DLC film,and (b)experimental curves of 6%La 2O 3doped DLC films fitted with two Gaussian lines.
Z.Zhang et al./Applied Surface Science 254(2008)7193–71977195
4.Conclusions
A novel kind of La 2O 3doped DLC films have been deposited by unbalanced magnetron sputtering.The intensities of PL and Raman spectra of the La 2O 3doped DLC films are higher than tho of pure DLC films,which suggests the optical properties of La 2O 3doped DLC films are improved.As the La 2O 3is stable within the DLC amorphous matrix,La 2O 3doped DLC films overcome the unstable property of single element within the DLC amorphous matrix,and their intensities of photoluminescence increa,so La 2O 3doped DLC films have potential promising for the application of solar cells.Acknowledgements
The authors appreciate the financial support from the Natural Science Foundation of Liaoning Province of China (Start up Foundation of Doctor)(Grant No.20071083),the Open Foundation of State Key Laboratory of Tribology of Tsinghua University (Grant No.SKLT0701),the Key Project of National Natural Science Foundation of China (Grant No.50535020),and the National Natural Science Foundation of China (Grant Nos.50575034,50675029,50575033and 50775021).References
[1]A.Grill,Thin Solid Films 355(1999)189.
[2]W.S.Choi,K.Kim,J.Yi,B.Hong,Mater.Lett.62(2008)577.
[3]M.J.Mirtich,D.Nir,D.Swec,B.Banks,J.Vac.Sci.Technol.A 4(1986)2680.[4]T.J.Moravec,J.C.Lee,J.Vac.Sci.Technol.20(1982)338.
[5]O.S.Panwar,B.Deb,B.S.Satyanarayana,M.A.Khan,R.Bhattacharyya,A.K.Pal,Thin Solid Films 472(2005)180.
[6]O.S.Panwar,Mohd.Alim Khan,B.Bhattacharjee,A.K.Pal,B.S.Satyanarayan,P.N.Dixit,R.Bhattacharyya,M.Y.Khan,Thin Solid Films 515(2006)1597.
[7]K.A.Hamouda,A.Ababou,M.Ouchabane,N.Gabouze,S.Belhous,H.Menari,K.Beldjilali,Vacuum 81(2007)1472.
[8]L.M.S.E.Deen,M.S.A.Salhi,M.M.Elkholy,J.Alloys Compd.465(2008)333.
[9]H.Lin,D.L.Yang,G.S.Liu,T.C.Ma,B.Zhai,Q.D.An,J.Y.Yu,X.J.Wang,X.G.Liu,E.Y.B.Pun,J.Lumin.113(2005)121.
[10]H.Chen,Y.H.Liu,Y.F.Zhou,Q.Y.Zhang,Z.H.Jiang,J.Non-Cryst.Solids 351(2005)3060.
[11]S.S.Kale,K.R.Jadhav,P.S.Patil,T.P.Gujar,C.D.Lokhande,Mater.Lett.59(2005)3007.
[12]Z.Y.Zhang,X.C.Lu,B.L.Han,J.B.Luo,Mater.Sci.Eng.A 454(2007)194.[13]Z.Y.Zhang,X.C.Lu,J.B.Luo,Appl.Surf.Sci.253(2007)4377.
[14]Z.Y.Zhang,X.C.Lu,B.L.Han,J.B.Luo,Mater.Sci.Eng.A 444(2007)92.[15]Z.Y.Zhang,X.C.Lu,J.B.Luo,Chin.Sci.Bull.52(2007)3292.[16]J.Robertson,Mater.Sci.Eng.R Rep.37(2002)129.
[17]X.Yu,C.B.Wang,Y.Liu,D.Y.Yu,Diamond Relat.Mater.15(2006)1223.
[18]Z.Y.Zhang,Z.Y.Jia,D.M.Guo,H.Gao,R.K.Kang,Surf.Coat.Technol.202(2008)3897.
[19]Z.Y.Zhang,X.C.Lu,J.B.Luo,Y.Liu,C.H.Zhang,Surf.Coat.Technol.202(2008)1621.
[20]Z.Y.Zhang,X.C.Lu,J.B.Luo,Y.Liu,C.H.Zhang,Diamond Relat.Mater.16(2007)1905.
[21]Z.Y.Zhang,X.C.Lu,J.B.Luo,Philos.Mag.Lett.88(2008)145.
[22]Z.Y.Zhang,X.C.Lu,D.M.Guo,J.Xu,J.B.Luo,Diamond Relat.Mater.17(2008)396.
[23]Z.Y.Zhang,X.C.Lu,J.B.Luo,T.M.Shao,T.Qing,C.H.Zhang,Chin.Phys.15(2006)2697.
[24]Z.Y.Zhang,X.C.Lu,J.B.Luo,Chin.Phys.16(2007)
3790.
Fig.4.(a)PL spectra of DLC and La 2O 3doped DLC films,and (b)PL spectrum of 6%La 2O 3doped DLC film fitted with four Gaussian
functions.
Fig.5.(a)Relative intensity ratio I D /I G ,G peak position,and (b)relative PL intensity obtained by taking the area of the broad band during the fitting of the PL spectra as a function of La 2O 3concentration in DLC films.
Z.Zhang et al./Applied Surface Science 254(2008)7193–7197
7196
[25]A.C.Ferrari,J.Robertson,Phys.Rev.B61(2000)14095.
[26]M.A.Tamor,W.C.Vasl,J.Appl.Phys.76(1994)3823.
[27]J.Schwan,S.Ulrich,V.Batori,H.Ehrhardt,S.R.P.Silva,J.Appl.Phys.80(1996)440.
[28]S.J.Henley,J.D.Carey,S.R.P.Silva,Appl.Phys.Lett.85(2004)6236.[29]B.Marchon,J.Gui,K.Grannen,G.C.Rauch,J.Ager,S.R.P.Silva,J.Robertson,IEEE
Trans.Magn.33(1997)3148.
[30]A.Y.Wang,K.R.Lee,J.P.Ahn,J.H.Han,Carbon44(2006)1826.
[31]J.K.Shin,C.S.Lee,K.R.Lee,K.Y.Eun,Appl.Phys.Lett.78(2001)631.
Z.Zhang et al./Applied Surface Science254(2008)7193–71977197
