Other important points

Page 1 To use other facilities at the center visit: http://csr.res.in

New Versatile facility at UGC-DAE CSR, Indore In-situ thin film Lab

- Chamber is equipped with a facility for thin film deposition using

electron beam evaporation with in-situ measurement of magneto

optical Kerr effect (MOKE), reflection high energy electron diffraction

(RHEED) and magnetoresistance (MR) measurements.

-Whole set-up is attached with a lab x-ray source coupled with a

multilayer optics, which provides a beam of sufficient collimation and

intensity to perform in-situ small angle x-ray reflectivity (XRR) experiments

in the laboratory.

-All the measurements in the present system can be done simultaneously

during and after the deposition of the film, thus making it possible to

study the evolution of magnetic, transport and structural properties with

parameter such as film thickness, annealing temperature etc.

-In contrast to the earlier in-situ systems in the literature, where

measurements with different techniques are performed separately and

results are interpreted by combining the data, in the present case,

combination of these techniques in a single set-up seems to be

promising in surface and interface analysis of magnetic thin films and

multilayer nanostructures.

In-situ characterization techniques

i. Magneto optical Kerr effect

(MOKE)

ii. Magnetoresistance (MR)

iii. Small angle X-ray reflectivity (XRR)

iv. Reflection high energy electron diffraction (RHEED)

Deposition using e-beam evaporation

Strength and Capabilities

UGC-DAE Consortium for scientific Research

Base pressure in the UHV

chamber ~2x10-10 mbar

Sample temperature ranging from

~50K to 1200K, which can be

precisely controlled during all in-

situ measurements

Ion gun at an oblique angle for

sample cleaning

Residual gas analyzer (RGA) to

monitor residual gasses present

before and during the deposition

Mass flow controller to create

partial pressure of the gases such

as O2 N2 Ar etc.

Dr. Dileep K. Gupta

Scientist In-situ thin film Lab

UGC-DAE CSR, Indore-452001

dkumar@csr.res.in;

dileep.esrf@gmail.com

Phone: +91-731-2463913 (ext.176)

Magnetic field for MOKE ~0.25 T

Sample temperature ranging from ~50K to 1200K

RHEED: 30 KeV electron gun

Page 2

In-situ MOKE, RHEED and XRR measurements of Co/CoO bilayer during Growth

Co/CoO bilayer structure was grown in UHV chamber at the base pressure of ~10-10 mbar using e-beam

evaporation technique. Growth of the bilayer sample was done on a silicon substrate in two steps; (i) deposition

of Co film at room temperature (ii) and formation of uniform oxide layer at the surface by heating it at 3000C in

a partial oxygen pressure 5 ×10-6 mbar.

During the growth of the bilayer, magnetic and structural properties were investigated in-situ using magneto-

optical Kerr effect (MOKE), Reflection high energy electron diffraction (RHEED) and X-ray reflectivity (XRR)

measurements.

It may be noted that MOKE and XRR measurements can be performed simultaneously whereas RHEED

measurements is performed after MOKE measurement in order to avoid deflection in electron due to magnetic

field generated by electromagnet during MOKE measurements.

An illustration of the versatility of the set-up

In-situ thin film Lab

RHEED image of Co

RHEED image of top CoO layer

0.4 0.8 1.2 1.6 2.0 2.4

75 min heating

50 min heating

10 min heating

Reflectivity (

arb

. units.)

2 theta

As prepared

-150 -100 -50 0 50 100 150

60 min

50 min

35 min

25 min

75 min

Inte

nsity (

a.u

)

H (Oe)

15 min Loop measurements

during surface oxidation process

-150 -100 -50 0 50 100 150

Inte

nsity (

a.u

)

H(Oe)

0, 45, 90 degree

Co film

as prepared

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

103

104

105

Co on Si

Si Subs

X-R

ay

In

ten

sit

y (

a.u

.)

Angle (Theta)

First row: RHEED, XRR and MOKE measurements after deposition of Co film on Si substrate. Hysteresis

loops in the last figure are taken at different azimuthal angle to get information of magnetic

anisotropy in the Co film.

Second row: all above mentioned measurements after surface oxidation of Co film. XRR and MOKE

measurements were carried also out during process of oxidation (after different time interval).

Page 3

Effect of Substrate Roughness on Growth of Thin Nanocrystalline Cobalt film

In-situ measurements jointly suggested that the films grow via Volmer-Weber growth process and proceed via

a nonmagnetic, superparamagnetic and a ferromagnetic phase on both the substrates. Islands were found

to coalesce at film thicknesses of ~ 0.6 nm and at ~ 1.5 nm for smooth and rough substrate respectively and

films become continuous and fully covering after the film thickness of ~1.5 nm and ~ 3.0 nm.

Thermal stability of W/Si and W/B4C/Si multilayers:

An illustration of the versatility of the set-up

In-situ thin film Lab

Growth of Co film on glass substrates with surface roughness of

0.5 nm and 1.6 nm has been studied in-situ using magneto-

optical Kerr effect (MOKE), reflection high energy electron

diffraction (RHEED) and four probe resistivity methods.

Representative loops with increasing Co layer thickness on [A]

=0.5nm and [B] =1.6nm substrate

Variation of sheet

resistance as a

function of Co

growth on rough

and smooth

substrate

-110 -55 0 55 110

(e)

(d)

(c)

(b)

(a)

Substrate

0.5 nm

0.7 nm

H (Oe)

1.1 nm

0.9 nm

(A)

-110 -55 0 55 110

(e1)

(d1)

(c1)

(b1)

(a1)

2.4 nm

2.2 nm

2.0 nm

1.8 nm

H (Oe)

(B)2.5 nm

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

sub

= 0.5 nm

sub

= 1.6 nm

RC

o (

k

/k)

d (nm)

0.0 0.4 0.8 1.2 1.6 2.0 2.4

X-R

ay I

nte

nsit

y (

a.u

.)

Angle (Theta)

W/B4C/Si Multilayer

0.0 0.4 0.8 1.2 1.6 2.0 2.4

X-R

ay

In

ten

sit

y (

a.u

.)

Angle (Theta)

W/Si Multilayer

In order to study the mechanism of diffusion in W/Si and W/B4C/Si multilayer, in-situ XRR measurements were

carried out upto high temperature annealing under UHV conditions. The temperature of the samples was

increased in the steps of ~200C from 2000C to 8000 C.

Sample structure

1. Si substrate W /B4C/Si- 10 bilayers

– bilayer thickness 4.3 nm

2. Si substrate W (1.7nm)/Si(2.4 nm)-

10 bilayers- bilayer thickness 4.1nm

It may be note that in case of W/B4C/Si

multilayer the height of the Bragg peak

does not change significantly even up to

8000C, whereas as in case of W/Si multilayer

it is significantly influenced after thermal

annealing. The present measurements

revealed that the addition of very thin layer

of B4C at interface of W and Si reduces inter-

diffusion between W and Si significantly.

NOTE: These samples were prepared using

ion beam sputtering technique in a

different chamber and finally transferred to

the UHV system for in-situ reflectivity. In-situ XRR pattern of a) W/B4C/Si multilayer and b) W/Si

multilayer at various temperatures ranging from 2000C to 8000C

Page 4

Attachment of Magneto-resistance (MR) option; growth of Ni film of Si substrate

In order to perform in-situ transport measurements, sample holder for four probe resistivity measurement has

been modified and tested by performing resistivity measurement during growth of Ni film. MR measurements

were also performed with increasing thickness of Ni layer. Experiments performed are shown below.

First figure gives the thickness dependence of film resistance (R). Initially up to a thickness of about 1.5 nm the

sheet resistance remains almost constant and essentially represents resistance of Si substrate. At this thickness,

the separation between Ni islands would be quite large and the conduction of electrons from one island to

another will not take place. With further increase in the thickness, as the islands come closer, hopping conduction

can take place, which results in a gradual decrease in the sheet resistance with thickness. Around a thickness of

about 2 nm a rapid decrease in the resistivity is observed, which signals the formation of a percolating cluster. In

the thickness range of 12–15 nm a continuous film is formed, and beyond this resistance exhibits a slow decrease

because of decreasing contribution of surface and interface scattering. Inset of Figure represents hysteresis loops

of Ni thin film at film thickness of 0.5, 2 nm and 20nm. One may note that at a thickness of 0.5 nm, hardly any loop

developed whereas a faint hysteresis loop starts appearing at around 2 nm thickness. The combined information

with MOKE revealed that near the film thickness of 2-3 nm, as the islands become multi-domain, the coercivity

starts developing. At very low thickness loop may be absent due to very small islands, which may be in single

magnetic domain and exhibit superparamagnetism. The present set-up also provides the capability to do MR

measurements at different azimuthal direction by rotating sample holder between the poles of the magnetic

field. Magneto-resistance (MR) measurements at thickness of 20 nm are also shown in figure.

An illustration of the versatility of the set-up

In-situ thin film Lab

Resistance and MOKE with Ni growth up

to 20 nm thickness

Magneto-resistance of Ni 20 nm thin film at

different azimuthal angle

Schematic view of sample holder prepared

0 4 8 12 16 20

0.2

0.4

0.6

0.8d= 0.5nm d= 20nm

Co

nn

ec

tin

g is

lan

ds

Re

sis

tan

ce

(k-o

hm

)

d (nm)

Island film Continious film

d= 2nm

-300 0 300

H (Oe)-300 0 300

H (Oe)

0

H (Oe)

00 20

010

0

300 40

0

80070

060

0

500

-225 0 225 -225 0 225 -225 0 225

Magnetic Field(Oe)

Volta

ge

of

the

sa

mp

le(V

)

Thin film

Au contacts

Page 5 Page 4

1. “Interface induced perpendicular magnetic anisotropy in a Co/CoO/Co thin-film structure: an in situ

MOKE investigation”

Dileep Kumar, Ajay Gupta, P. Patidar, A Banerjee, K K Pandey, T. Sant and S. M. Sharma, J. Phys. D: Appl.

Phys. 47 (2014) 105002; doi:10.1088/0022-3727/47/10/105002

2. “In situ surface magneto-optical Kerr effect (s-MOKE) study of ultrathin soft magnetic FeCuNbSiB alloy

films”

Dileep Kumar, Pooja Gupta, and Ajay Gupta, Materials Research Express 1 (2014) 046405;

doi:10.1088/2053-1591/1/4/046405.

3. “Correlation between iron self-diffusion and thermal stability in doped iron nitride thin films”

Akhil Tayal, Mukul Gupta, Dileep Kumar, V. R. Reddy, Ajay Gupta, S. M. Amir, Panagiotis Korelis, and

Jochen Stahn, Journal of Applied Physics 116, 222206 (2014); doi: 10.1063/1.4902962.

4. “Study of ultrathin magnetic cobalt Films on MgO(001)” Gagan Sharma, U.P. Deshpande, Dileep Kumar

and Ajay Gupta Journal of Applied Physics 112, 023910 (2012).

5. “In-situ study of magnetic thin films on nanorippled Si (1 0 0) substrates”

Sarathlal K.V., Dileep Kumar, V. Ganesan, Ajay Gupta, Applied Surface Science 258 (2012) 4116

6. “Study of Co90Fe10 magnetic thin Film on MgO substrate using In-situ MOKE Technique”

Gagan Sharma, Dileep Kumar, Ajay Gupta

Journal of Physics: Conference Series 365 (2012) 012038

7. “Growth study of Co thin film on nanorippled Si(100) substrate”

Sarathlal K. V., Dileep Kumar, and Ajay Gupta, Appl. Phys. Lett 98, 123111 (2011)

Related Publications

In-situ thin film Lab

Dr. Dileep K. Gupta

Scientist In-situ thin film

UGC-DAE CSR, Indore-452001 dkumar@csr.res.in; dileep.esrf@gmail.com

Phone: +91-731-2463913 (ext.176)