Quan i ica ion o he H con en in diamondlike ca bon and polyme ic hin
ilms by e lec ion elec on ene gy loss spec oscopy
F. Yube o,a兲V. J. Rico, J. P. Espinós, J. Co ino, and A. R. González-Elipe
ICMSE (CSIC-USE) Amé ico Vespucio s/n, E-41092 Se illa, Spain
共Recei ed 24 Ma ch 2005; accep ed 28 June 2005; published online 15 Augus 2005兲
A nondes uc i e me hod o de e mine he hyd ogen con en a he su ace o diamondlike ca bon
and polyme ic hin ilms is p oposed. The me hod elies on he analysis o he elas ic peak p oduced
by backsca e ing o elec ons om he hyd ogen a oms p esen a he sample su ace. Quan i a i e
analysis o he H con en a he su ace is achie ed h ough use o a phenomenological sensi i i y
ac o o elas ic elec on backsca e ing by H a oms wi h espec o o he a oms p esen a he
su ace o e e ence polyme ic samples. The alidi y o he me hod is checked wi h elas ic ecoil
de ec ion measu emen s and in a ed spec oscopy analysis o he same samples. The accu acy o
he me hod in he de e mina ion o H con en a he sample su ace is es ima ed o be ±10%. © 2005
Ame ican Ins i u e o Physics.关DOI: 10.1063/1.2011786兴
Quan i ica ion o he hyd ogen con en in diamondlike
ca bon 共DLC兲and polyme ic hin ilms is o he mos impo -
ance because hei p ope ies a e igh ly linked o his
con en .1Typically he hyd ogen con en in his ype o ma-
e ials has been de e mined wi h echniques such as elas ic
ecoil de ec ion analysis 共ERDA兲, nuclea eac ion analysis
共NRA兲using he 1H共15N,
␣
兲12C nuclea eac ion, nuclea
magne ic esonance 共NMR兲, he mal hyd ogen e olu ion, o
in a ed spec oscopy 共IR兲. Conscious o he g ea demand o
al e na i e and simple me hods,1–3 we ha e de eloped a p o-
cedu e o quan i y he hyd ogen con en a he su ace o
DLC and polyme ic hin ilms. As i will be shown in his
pape , he H con en wi hin he su ace egion o hese ype
o ma e ials can be de e mined by looking a he elas ically
backsca e ed elec ons wi h kine ic ene gies in he o de o 1
o 2 keV as in s anda d e lec ion elec on ene gy-loss spec-
oscopy 共REELS兲analysis. The basis o he quan i ica ion is
he same as ha o Ru he o d backsca e ing spec oscopy
共RBS兲, wi h he di e ence ha in RBS he p obe pa icles
a e usually alpha pa icles and in ou me hod elec ons 共no e
he di e ence o mass be ween hese wo p ojec iles兲. In his
espec , i mus be men ioned ha e y ecen ly O osz e al.4
ha e epo ed ha H a oms in polye hylene can be de ec ed
by his echnique. I is also wo h men ioning ha REELS
was used in he pas o de ec H induced chemical shi s in
he plasmon exci a ions.5
The p esence o H can be easily de ec ed by s anda d
REELS measu emen s wi h 1 o 2 keV elec on beams. The
physical basis o he de ec ion o H a oms a he su ace o
ma e ials con aining ligh elemen s is he expec ed di e ence
in he ecoil ene gy ⌬E
6in he in e ac ion o a as elec on
wi h a s a ic nucleus, ei he hyd ogen o ano he ype o
a om, which can be es ima ed by he exp ession
⌬E =4me
MH
E0sin2
␪
2
冉
1− 1
A
冊
,共1兲
whe e me,MH, and Aa e he elec on mass, he a omic
weigh o he H a om and he o he nucleus conside ed, e-
spec i ely,
␪
is he sca e ing angle, and E0is he p ima y
ene gy o he incoming elec ons. This exp ession p edic s
ha , o a ypical sca e ing angle o
␪
=120° and a p ima y
ene gy o 1500 eV, he di e ence in ecoil ene gies be ween
H and o he a oms hea ie han C is ⬃2.1 eV, so ha we
migh easily dis inguish be ween H and hese o he a oms
p esen in he sample wi h he s anda d ene gy esolu ion o
REELS measu emen s 共i.e., ew en hs o eV兲.
Figu e 1 shows he REELS spec a, aken wi h a p ima y
elec on beam o 1500 eV, o se e al e e ence samples
关polyca bona e 共PC, -C16H14O3-兲, polys y ene 共PS, -C8H8-兲,
polyme hyl-me hac yla e 共PMMA, -C5H8O2-兲, and poly e -
a luo e hylene 共PTFE, -CF2-兲and highly o ien ed py oli ic
g aphi e 共HOPG, C兲兴. The REELS measu emen s we e pe -
o med wi h special ca e o minimize elec on damage a he
su ace o he samples. Thus, ypically he measu ing ime
was o ⬃1 min. wi h elec on beam cu en s below
1
␮
A/cm2.7The angle o incidence o he elec on beam
wi h espec o he su ace no mal was 60° 共i.e.,
␪
=120°兲and
he elec on de ec ion was se no mal o he sample su ace.
In he elas ic egion o hese spec a 共be ween ⬃1497 and
1502 eV兲 he H signal can be clea ly iden i ied as a weak
peak a 2.1 eV lowe kine ic ene gy han he mo e in ense
ea u e in he spec a a 1500 eV. This la e peak is due o he
elec ons backsca e ed by he a oms o he han H p esen a
he su ace o he samples. No e ha he small peak a 2.1 eV
is only p esen in he H con aining polyme s 共i.e., PS,
PMMA, and PC兲and is no de ec ed in he case o PTFE o
HOPG, as expec ed. This peak shi s o 3.0 eV lowe kine ic
ene gy han he main peak when he exci a ion ene gy is
changed o 2000 eV 共no shown兲. This esul con i ms i s
assignmen as elec ons backsca e ed by he H a oms in he
samples. A his poin i is wo h men ioning ha using p i-
ma y beam ene gies la ge han ⬃1800 eV has he e ec o
inc easing he backg ound be ween he wo con ibu ions o
he elas ic peak p obably due o mul iple elas ic sca e ing
and damage. On he o he hand, he wo con ibu ions o he
elas ic peak do no sepa a e enough o acili a e quan i ica-
ion when p ima y elec on ene gies smalle han ⬃1200 eV
a e conside ed. Besides he small ea u e a ⬃2.1 eV om
he main elas ic peak o E0=1500 eV, hese spec a a e
cha ac e ized by he ypical
␲
plasmon ea u es a ⬃6eV
ene gy loss, co esponding o he benzoic ings in PC and
a兲Au ho o whom co espondence should be add essed; elec onic mail:
[email p o ec ed]
APPLIED PHYSICS LETTERS 87, 084101 共2005兲
0003-6951/2005/87共8兲/084101/3/$22.50 © 2005 Ame ican Ins i u e o Physics87, 084101-1
12 June 2025 14:52:16
PS, and o he sp2cha ac e o g aphi e. Besides, he co e-
sponding
␴
+
␲
bulk plasmons a e indica ed o each ma e-
ial. All hese e e ence samples we e also analyzed by XPS
o con i m he le el o su ace con amina ion. I was ound
ha a 5%–10% o O con amina ion was p esen a he su -
ace o polyme s ha do no con ain oxygen in hei s uc-
u es. A simila de ia ion om he heo e ical oxygen con en
was ound in hose ma e ials such as PC o PMMA ha
con ain his elemen in hei s uc u es.
F om he ela i e in ensi y o he H peak wi h espec o
he main ea u e o he spec a, i is possible o es ima e a
phenomenological sensi i i y ac o
␴
exp ha , in he o m o
a calib a ion cu e, se es o co ec o he di e en c oss
sec ions o elas ic elec on backsca e ing by H o o he a -
oms 共C and, o a mino ex en , O a oms兲p esen a he su -
ace o he polyme s. The inse in Fig. 1 shows he co ela-
ion be ween he in ensi y a io IH/Ino_H, and he nominal
a io be ween H and o he ype o a oms 共C and o O兲p esen
in he polyme s conside ed in his s udy. He e IHis he a ea
o he H signal in he back e lec ed elec ons and Ino_His he
a ea o he elas ic peak coming om a oms o he han H. I
can be obse ed ha he e exis a linea co ela ion wi hin
he expe imen al unce ain ies be ween he nominal a omic
a io and he expe imen al in ensi y a io. In his analysis, we
did no a emp quan i ica ion o high-H con en polyme s
such as polyp opylene 共-C3H6-兲o polye hylene 共-CH2-兲be-
cause hey a e known o deg ade easily wi h elease o hy-
d ogen when hey a e bomba ded wi h low-ene gy
elec ons.7By pe o ming a linea eg ession passing h ough
he o igin o coo dina es wi h he o he poin s in he g aph,
he slope o he i ed line is 37. This alue can be conside ed
as a phenomenological ela i e c oss sec ion
␴
exp be ween
he wo con ibu ions o he elas ic peak signal. No e ha he
alue ob ained o
␴
exp is in easonable ag eemen wi h he
p edic ions o he NIST da abase o elas ic sca e ing c oss
sec ions8共neglec ing he p esence o oxygen a oms a he
su ace and mul iple elas ic sca e ing, ha may be signi i-
can in his case9兲. A ough heo e ical es ima ion o
␴
exp is
42, ob ained as he a io o he di e en ial elas ic sca e ing
c oss sec ion wi h espec o he solid angle be ween C and H
o 120° sca e ing angle and 1500 eV elec on ene gy.8In
he ollowing we will used ou phenomenological
␴
exp=37 o
quan i y he H con en in DLC samples. Thus, he H quan i-
ica ion a he su ace o unknown samples by REELS can be
pe o med acco ding o he exp ession
%H= 100 IH
␴
exp
IH
␴
exp +Ino_H
,共2兲
whe e he meaning o he di e en magni udes has been in-
oduced p e iously.
To check he alidi y o his p ocedu e, a i s compa a-
i e s udy was ca ied ou by ERDA/RBS and REELS o a
se ies o DLC samples p epa ed wi h ixed bias ol age and
di e en con en o H in he plasma gas. The DLC hin ilms
we e p epa ed by plasma Enhanced Chemical Vapo Deposi-
ion in a plasma eac o wi h a pla e con igu a ion. Mix-
u es o C2H2, A , and H2we e used as he plasma gas, while
a sel -induced bias ol age was applied o he pla e elec ode
con aining he subs a e o he samples. I was ound ha he
pe cen age o H a oms in he DLC ilms measu ed by bo h
echniques 共no shown兲was he same wi hin 10%, so ha ,
wi h he unce ain y limi s o hese echniques, hey yield
simila alues o he H con en o he ilm. This p o es ha
REELS can be an al e na i e echnique o he de e mina ion
o H con en a he su ace in DLC ilms.
To check u he he alidi y o he me hod, he hyd o-
gen con en has been also de e mined o a se ies o DLC
hin ilms p epa ed wi h a s anda d plasma composi ion by
a ying he bias ol age applied o he subs a e pla e. Bias
ol age is ecognized as a c i ical pa ame e o he con ol o
he ha dness and o he p ope ies o DLC hin ilms.10 Fo
his se ies o samples, he pe cen age o hyd ogen in he
ilms has been plo ed in Fig. 2 agains he bias ol age. Fo
compa ison, his igu e also includes he e olu ion o he
in ensi y o he 2750–3050 cm−1 IR band, co esponding o
he s e ching C-H ib a ions, no malized o he ilm hick-
ness as de e mined by x- ay luo escence spec oscopy in a
scanning elec on mic oscope. I is in e es ing ha , wi hin
he e o ba s in bo h p epa a ion and quan i ica ion p o o-
FIG. 1. REELS spec a measu ed wi h 1500 eV kine ic ene gy o PTFE,
g aphi e 共G兲, PC, PS, and PMMA. Inse : Co ela ion be ween he heo e ical
H con en in he e e ence polyme samples and he a io IH/Ino_Has de e -
mined by REELS measu emen s.
FIG. 2. Co ela ion be ween he no malized in ensi y o he in a ed C-H
s e ching modes, accele a ion ol age du ing p epa a ion and he a omic
pe cen age o H in he ilm as de e mined by quan i ica ion o he elas ic
signal in REELS da a. Full ci cles: In a ed quan i ica ion; open squa es:
REELS quan i ica ion.
084101-2 Yube o e al. Appl. Phys. Le . 87, 084101 共2005兲
12 June 2025 14:52:16
cols, hese wo magni udes ollow simila endencies. This
e olu ion is cha ac e ized by a p og essi e dec ease in he
hyd ogen con en as he bias ol age inc eases. This co ela-
ion shows ha , despi e he su ace cha ac e o REELS, i s
quan i ica ion da a o hyd ogen can be aken as oughly ep-
esen a i e o bulk composi ion.
To conclude, he p esen esul s ha e shown ha REELS
may p o ide a way o quan i ying he amoun o hyd ogen
p esen a he su ace o DLC o polyme ic ma e ials whe e
C and H a e he majo i y cons i uen elemen s. The su ace
cha ac e o REELS is con olled by he mean ee pa h o
elec ons ha a el h ough he analyzed ma e ials ha , o
he usual elec on ene gies u ilized in his echnique, is
⬃3 nm. We wan o emphasize ha his analysis p ocedu e
measu es di ec ly he amoun o hyd ogen by a su ace sen-
si i e echnique. I could hus be use ul o combine REELS
wi h XPS o su ace analysis since XPS does no di ec ly
de ec H.
We hank he Spanish Minis y o Science and Educa ion
共MAT2004-01558兲 o inancial suppo .
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