Study of surface segregation and roughness using

synchrotron radiation

A. Iraji zad

3.SESAME users’ meetingAntalya 2004

Physics Department, Sharif University of Technology, Tehran, Iran

outline

• Introduce some of our results on Cu surface segregation • Plan for further study using SR• Other fields surface roughness measurement using AFM and light scattering interface roughness photoinduced nanoparticle formation porous silicon as gas sensors

Surface segregation of copper

We have observed Cu at the surface of

• V2O5/Cu/Si bi layers during room temperature deposition

• Ni/Cu/Si and Permalloy/Cu/Si multilayers after Electrodeposition

• Applications: solid state Li battery,

Giant magnetoresistance (GMR), spin valve

Cu

Deposited layer

Segregated Cu

Si

AES spectra of V2O5 (100nm)/Cu

A Iraji-zad et al; J. Phys. D: Appl. Phys.; 35 (2002) 1176

Cu top layer should be very thin.

Depth profile using SIMS tech.

V2O5 (100nm)/Cu(200nm) /Si sample

10.00

100.00

1000.00

0.00 0.50 1.00 1.50

Sputtering Time (1000 s)

co

un

ts

Cu

V

Segregated Cu

M. M. Ahadian, A. Iraji zad, “Structure and composition of the segregated Cu layer in V2O5/Cu/Si system”, submitted to Applied Surface Science

Surface electronic properties using Tunneling Spectroscopy

V2O5(100nm)/Cu/Si and V2O5 (100nm)/Si samples

The segregated Cu changes the electronic surfacelocal density of states from semiconductor to metallic behavior

Surface topographyThe effect of segregated Cu ( Presence of Cu under layer)

Cu segregation in Ni/Cu and Ni-Fe/Cu samples SIMS results on permalloy(200nm)/Cu

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1.00E+07

1.00E+08

0.00 0.20 0.40 0.60 0.80 1.00

Ni

Cu

FeO

NiO

Sputtering time (a.u.)

Segregated Cu

glow discharge optical spectroscopy of Ni(100nm)/Cu/Si

0.00

1.00

2.00

3.00

4.00

0 2 4 6

Cu

Ni

Sputtering time (s)

cou

nts

(a.

u.)

AES result of electrochemical deposited

Ni(100nm)/Cu

The accumulation of Cu at the surface

Counts

Kinetic Energy, eV620 720 820 920

32000

34000

36000

38000

40000

42000

44000

46000

48000

50000

Cu

LM

1C

u L

M2

Cu

LM

5

Cu

LM

6Cu

LM

7C

u L

M8

Cu

LM

9

Ni L

M1

Ni L

M2

Ni L

M3

Ni L

M4Ni L

M5

Ni L

M6N

i LM

7N

i LM

8

Ni L

M9

M.M. Ahadian, A. Iraji-zad, A. G. Dolati, M. Ranjbar, “Induced segregation of Cu in permalloy thin films

produced by electrochemical deposition”, in preparation

XPS result for electrochemical deposited Ni(100nm)/Cu

XPS & AES indicate the chemical state of Cu at the surface: Cu2O

Uniform Ni layer

Counts

Binding Energy, eV970 958 946 934 922

3800

4200

4600

5000

5400

5800

A

B

Cu

2p

1

Cu

2p

3

Summary of the first part• Cu segregation occurs in both systems during

room temperature deposition.

• We should know Cu depth profile near the surface to understand this phenomenon

• Destructive depth profile methods alter the profile.

XPS method is a non-destructive method depth profile measurement by– Changing incident X-ray energy– Changing incident angle

Conventional XPS represents a severe limitation

Synchrotron radiation source is needed for better depth profile

measurement.

E Photoelectron= hע- Binding Energy

inelastic mean free path of electron depends on the electron energy

By changing the energy of incident X-ray, depth profile is possible:

e.g. Al at the surface of zeolite

Depth profile of carbon chemical state

Surface roughness measuremente.g. dynamic behavior of growing surface, interface effects

– Methods : SPM, photon scattering,…

– Interfacial roughness changes the

physical properties of multilayer systems

e.g. GMR, QW, spin valves,…..– Antiferromagnetic coupling is dependent on the interfacial structure,

A. Iraji zad, et al, Height fluctuation and intermittency of V2O5 films by atomic force

microscopy , Journal of Physics Condensed Matter, 15, 2003, pp. 1889-1898

B. Stochastic and regeneration of rough surface, Phys. Rev. Lett., 91: (22), 226101-1-226101-4,.2003

AFM as surface profilerstatistical parameter

Disadvantage: slow,Tip effect, surface damage,…..

Advantage: A direct method, good information on lateral scale

visible light scattering topographyvisible light scattering topographyfastfast, , no information on lateral scale, information in micron sizeno information on lateral scale, information in micron size

G. R. Jafari, P. Kaghazchi, R. S. Dariani,A. Iraji zad, S. M. Mahdavi, M. Reza Rahimi Tabar and N. Taghavinia, Non-Pertubative Two Scale Kirchhoff Theory: Comparison of Experimental Observations with Theoretical Prediction , is submitted to Physical Review B, 2004

PMT

Las

er

Soft X ray scattering provide better information of surface and

interface roughness

Ni

Cu

Si

Interface roughness measurement by AFM

Small angle x ray scattering (SAXS)

and Grazing Incidence GISAXS good for Q dot

structure

h: roughness exponentLabat et al , Applied Surface Science, 188,2002,p182

SAXS for CoFe/Cu multilayer at different X-ray energy

Anodic Aluminum oxide (AAO):Fabrication, Mechanisms and Characterization

as a starting material for the fabrication of several kinds of functional devices with nanometer dimensions like catalysts, filters, magnetic recording media ,….

nanowire in AAO next step: formation of spin valve by

electrodeposition

Farzad Nasirpouri, Mohammad Ghorbani, Azam Irajizad, Amir Mehdí Saedi, Alain Nogaret, Growth sequences of highly ordered nano-porous anodic aluminium oxide, Trends in Nano technology (TNT2004), Spain, sept. 2004

Next step: Structural studies

• SAXS (small angle), X ray diffraction

• Pore characterization in the range 2-200 nm

• EXAFS provide information on oxidation state

Photochemical method

Illumination is the main parameter for reaction progressing.

Zn(SO4) Na2S

ZnS

Capping agent molecules usually used to keep the sizes small.

A photochemical based method for nanoparticle synthesizing and formation

e.g. CdS nanoparticle

Chemical method

0 2 4 6 8 103.00

3.05

3.10

3.15

3.20

3.25

3.30

3.35

3.40

2.6

2.8

3.0

3.2

3.4

3.6

Ba

nd

ga

p(e

v)

Time(min)

Siz

e(n

m)

Fig 2. Band gaps and sizes of the samples versus illumination time that are prepared with surfactant concentration of 0.5 Mol/lit

A photochemical method for controlling the size of CdS nanoparticlesM. Marandi, N. Taghavinia, A. Iraji-zad, S. M. Mahdavi, and M. R. Esmaili,is submitted to nanotechnology

Adjustable parameter

Illumination time, density of surfactant and PH of the solution

Photoinduced nanoparticles growth: size control by UV illumination, Nima Taghavinia, Azam Iraji zad, Mohammad Mahdavi and M. Reza Esmaili, submitted to Jounal of Nanoscience & Nanotechnology.

TEM image of the samples with effective band gap of 3.4

Light surface interaction

• Surface etching

• film deposition e. g. Ni , Pd

• Nanoparticle formation e. g. Au

• Particle size controling

50 m

PPS p type N type

P type

Chemical etching the Si surface

Gas sensors based on porous silicon

• Chemical ecthing +Pd nano particle deposition by electroless method as hydrogen sensitive

A.Iraji zad1, F.Rahimi, M.Chavoshi, M.M.Ahadian , Characterization of porous poly-silicon as a gas

sensor, Sensor and Actuators B, 100( 2004) 341-346

•

• Wet deposition Synchrotron x-ray can induced electroless metal deposition useful for microelectronics

and x ray optics

• or etching over the solid surfacesSelected area

• new material processing method, rapid maskless patterning technique.

• Nano particle formation

Borse et al, pH dependence of synchrotron x-ray induced electroless nickel deposition, JAP, 95,3,2004,p 1166

Conclusion

• Synchrotron radiation is a valuable source in our future research

• Possible to determine Thickness, composition, depth profile of segregated Cu

Surface roughness measurement in nano scale

Interface roughness determination in multilayer systems

Light assisted nanoparticle formation & synthesis

size controlling, deposition and etching

• Need in access , collaboration and contribution

• Need to train potential users as well as operators, designers,….

acknowledgment

PhD students• M. M. Ahadian• M. Marandi• F. Rahimi• R. Tilaki• F. Nasiripouri• G. Jafari

• M. R. Rahimi Tabar • N. Taghavinia• S. M. Mahdavi• M. Dolati• M. Gorbani