PES study of amorphous alloy Fe40Ni40P20

Solid State Communications,Vo1.60,No.9, Printed

pp.701-704,

0038-1098/86 $3.00 + .OO

1986.

Pergamon

in Great Britain.

PES STUDY OF AMORPHOUS JiMingrang.~Jiamcin.& University

Journals

Ltd.

ALLOY Fe 40Ni40P20 Zbsnhui,zhangQirui

of Science and Technology of China,Hefei,China (Received 20 August 1986 by W.Y. Kuan)

The electron structure of amorphous Fe4ON14OP20 has been investigated before and after annealing by XPS and UPS (HeI,HeII).It is shown that the spectra of UPS were modified obviously by various degree of annealing.Composition and chemical states of the components on the surface of the sample are also presented and the effect of structural ordering on the density of states (DOS) of the valence band is discussed.

l.Introduction Various physical and chemical properties of amorphous alloys are very different from that of crystalline counterparts.It is well known that the properties of crystals are strongly dependent upon their electron structures.The situation for amorphous alloys has been reviewed by 0elhafenl.A remarkable effect of electronic structure on properties exist, especially the structure of valence band. Therefore a direct comparation of electron structures between crystalline and amorphous state is helpful to understand them.In the present work we aim at the investigation of electron structure of amorphous Fe4ONi4OP20 and the effect of annealing at different conditions on the valence band structure and on the composition,as well as on the chemical states of the surface by means of XPS and UPS (HeI,HeII). Z.Experimental The sample was prepared using meltspinning technique.After isopropyl alcohol cleaning,the sample was transferred into electro-spectrometer ESCALAB MK-11,in which the pressure was about 2x10-10 mbar.Composition and chemical states of the original surface were examined by XPS with Mg K, X-ray source (-1253.6eVj.Then the sample was sputtered by argon ion with the energy of 1.5KeV and target current of 30rA.the same examination was carried on after different time of sputtering until no contaminations of carbon and oxygen can be detected. With the sputter-cleaned surface of the sample spectra of valence band (VB) were taken using UPS He1 (-Zl.ZeV),HeII (-40.8eV) and XPS with monochrometic Al Km X-ray source ( 1486.6 eV) respectively.After that crystallization was obtained in-situ by annealing at different temperatures followed by VB spectra acquisition with the same parameters as those of previously used,and the composition and chemical states were also monitered by XPS during annealing. 3.Results and Discussion The composition and chemical states of the original surface of the sample Fe4ONi4OP20 are quite different from those of the bult,as shown in Fig.1 and Fig.2. Fe and P are concentrated on the original nature surface.Fe exists in the state of oxide

0

6 Etching

Time

12 (min.)

18

Fig.1. Varity of surface composition with Ar+ 1.5Kev.Target etching time.The Ar+ energy current-30&A.

(Fe203) while P in two kinds of chemical state, one is element-like P and the other seems to be the oxide of it.Ni is hardly detectable. After about three minutes of sputterring,concentration of Fe decreased and t!xt of Ni increased,the composition changed obviously towards the original concentration of the cornPonents Of the sample.Fe is in the chemical States of mixture of metal-like Fe and its oxide.P turns into only one state of elementlike P.Their binding energies of core levels are listed in Tab.l.The similar state of the

Table

1. Eb of core level of components in Fe4ONi4OP20

element

FeZp3/2 (eV) 706.8

Ni2p3/2 (eV) 852.6

~:~~~i~'

710.5

852.9

706.9

852.9

129.3

706.9

852.9

129.4

Core

level

Pure Amorphous

Ar+sputtered state surface Crystalline state 701

P2P (eV) 129.63 133.2 129.3

702

PES STULIY OF AMORPHOUS I

-

I

-

& ,. -....

..: J”‘.._._, : ., : .i’ ?. I . ‘\

-,

.I

.,

.. :

Fe

ALLOY Fe

40

Ni

P 40 2c!

I,

Vol. 60, No. 9

I

I.. (1 )

2p

.:

.’ ..:

.. ..

’ Mg K

:

.70x.0

708.0

713.0

718.0

723.0

728.0

(a)

Mg K

126.0

128.5

131.0

133.5

136.0

138.5

(b) Binding

Energy

(ev)

Fig.2. Varity of chemical states of Fe P (b) with sputtering time.(l) Original fate;(2) After 3 minutes sp"ttering;(3) 21 minutes sputtering:The Ar+ energy 1 Target current -3OuA.

surface lasted 20 minutes of sputtering time and the atomic ratio of Fe:Ni:P got stable at approximately 44:34:22.It should be mentioned that in our case the prefersputter-effect is not serious with relatively low energy of argon ion according to the sputtering yield after Seah2.

a) and surAfter 5KeV.

After exposing the sputter-cleaned Surface to the air for about two weeks.the result of XPS showed that the composition and chemical states of the surface had become similar with those of the original nature surfaCe.So we can say that the migration of Fe and P to the surface of the amorphous alloy are mainly

PES STUDY OF AMORPHOUS

Vol. 60, No. 9

it is not available.The results of our oxperiment agree with Moruzzi5 Who suggested that transition metal glasses tend to have large DOS at Fermi level. It is known that annealing may cause modifications of structure,composition and/or chemical state.All these can affect the struc-

due to the chemical driving force of the OXidation of them.But the oxidized layer is very thin and protests the alloy from further oxidation. The valence band spectra of XPS and UPS He1 and He11 are shown in fig.3 (a) (b) (c) respectively.

mono-Al

703

ALLOY Fe40Ni40P20

He11

K

/ i

, 0.0

,

.

,

,

.

, 6.0

3.0

,

.

, 9.0

I

I

*

0.0

1 5.1

t

I

1

I

10.2

I

1s

a.. 0.0

Binding

Energy

I.

8.0

I.

12.0

I

16.0

Cc)

(b)

(a)

8. 4.9

(eV)

Fig.3. Comparation of valence band spectra of XPS (a),UPS He1 (b) and He11 (c) of the amorphous and different degree annealed Fe4ONI4OP20 with those of the pure metals Fe and Ni.(l) Pure Fe;(Z) Pure Ni;(3) The amorphous;(4) 4OO"C,20 minutes annealed:(5) 450°C. 20 minutes annealed;(6) 51O"C.ZO minutes annealed.

The main feature of these XPS spectra looks very similar,but both the UPS spectra of He1 and He11 were modified obviously by annealing.Starting from annealing at 400°C for 20 minutes,the density of state (DOS) at Fermi level,which is from unbended d-electron of Ni and Fe,decreased and the DOS at lower energy of -6 to -lOeV,which is mainly from the bonded d-electron of the metals with the p-electron of the metalloid P,increased.This trend of modification is getting more obvious with increasing degree of annealing. According to the free electron model by Nagel and Tauc4. the DOS at Fermi level is minimum in amorphous state.In our case,however,

ture of valence band.The composition and chemical states were monitored by XPS in all the duration of annealing.In Fig.4 and table 1 it is shown that the composition and chemical states of the sample surface almost kept unvariable during the annealing.That means the variation of valence band structure mentioned above is mainly due to the structure ordering through annealing.As we know that after crystallization the "final state effect" of photoionization will also exert an influence on the structure of UPS.In table 1 we can see the binding energies of FeZp3/2,Ni2p3/2 and P2p in crystalline state are 706.9eV.852.9eV and 129.5eV respectively,which are nearly same

704

PES STUDY OF AMORPHOUS 100 Fe 80 -

Ni P

60 cho z 40 1,

II

.

. I

3:

20,;

.

.

A

450

510

0 RT

h '( 400 Annealing

temp.("C)

Fig.4. Varity of surface composition at different annealing temperatures for 20 minutes. with those in the amorphous state.This is consistent with the conclution that the chemical short range order exists in amorphous alloy. The binding energy deviations of the core levels of Fe and Ni in the alloy from those of the pure metals are +O.leV and t0.3eV respectively.This could be taken as an indication that in amorphous alloy the interaction between Ni and P is stronger than that betleen Fe and P.It is against the theoritical result by Messer6.

ALLOY Fe40Ni40P20

Vol. 60, No. 9

After collection of the spectra of the sample annealed at 51O'C for 20 minutes,argon ion sputteringwas executed with the energyof KeV for 18 minutes to remove the surface layer and the VB spectra were taken again.We found that the spectra returned to those of the amorphous state.X-ray diffraction confirmed that the sample had returned to amorphous state.We can say that the crystallization started from the very surface of the sample. And the sampling depth of XPS for VB is larger than that of UPS,so it is expected that the VB spectrum of XPS is less sensitive to the surface crystallization than that of UPS. 4.Conclusions (1) In the amorphous Fe4ONi4OP20,Fe and P are concentrated on the original nature surface,and Fe exists in oxide state and P is partially oxidized and Ni is hardly detectable. (2) The DOS at Fermi level was getting decreased along with the development of structural ordering,while the binding energies of the core levels of the component metals were unchanged,and the composition of the surface kept constant as well. (3) Crystallization started from the surface of the sample and developed deeper with the increasing degree of annealing,and UPS is sensitive to the surface crystallization. (4) The interaction between Ni and P is stronger than that between Fe and P in the alloy Fe4ONiPOP20.

References

l.P.Oelhafen,Glass Metals 11,chapter 9 (1983). Z.D.Briggs and M.P.Seah,Practical Surface Analysis,213 (1983). 3.C.D.Wagner,W.M.Riggs,J.F.Moulder and G.E.Mailenberg (editor),Handbook of X-ray Photoelectron Spectroscopy (1979).

4.S.R.Nagel and J.Tauc,Phys.Rev.let?r 35, 380 (1975). 5.V.I.Moruzzi.P.Oelhafen and Jr.A.R.Milliams, Phys.Rev.B Vo1.27,No.12,7194 (1983). 6.R.P.Messmer.Phys.Rev.B Vo1.23.No.4.1616 (1981).