It is a presentation in front open audience about the research work some one does in his phd career before six months of the Synopsis seminar.

1. Nanopatterning of CoSi binary material
using low energy ion beams
Basanta Kumar Parida
Department of Physics
IIT Ropar
Open Seminar

2. Patterns
Source (google)2/23/2019 2

3. Outline
2/23/2019 3
• Nanopatterning
• Ion beam nanopatterning
• Historical overview
• Single elemental system
• Binary and compound systems
• My work
• Experimental details
• Instability driven pattern formation
• Influence of ion species and composition
• Electrical measurement on higher ordered nanoripples
• Influence of swinging on morphology evolution
• Summary

4. Nanopatterning
2/23/2019 4
Nanopatterning
Approaches
Top-down
Photolithography
e-beam lithography
Writing,
stamping
Bottom-up
Growth
phenomena
Spontaneous
assembling
Rawat J. Phys Conf Ser. (2015) Source(google)
Electron Beam Lithography
UV-Nanoimprint Lithography
Methods to manufacture nanomaterials or pattern materials on a nanometre scale

5. Ion beam nanopatterning
Advantages
• Single step process for large area self-
organized nanopatterning
• Faster and cheaper compared to
conventional lithographic techniques
• Easily tunable process parameters
• High spatial selectivity
• Any ion beam can be put into any matter
• Maskless process, less time
• Not require ultra high vacuum
• Nanoripples and dots
2/23/2019 5
Applications of these nanopatterns
Optoeletronic devices, funcionalized surface,
plasmonic, magnetic applications
Before irradiation
Ar+ 500 eV, 67o,15 min→Si
After irradiation

6. Our
work
Ion beam nanopatterning
2/23/2019 6
Ion beam
nanopatterning
Single
element
Binary
compound
Pure binary
50-50 %
Impurity assist
to single
element

7. First observation… (nanoripples and dots)
4 kV Air  glass
0o
420 eV Ar+  GaSb
S. Facsko et.al., Science, 285, 1551 (1999)Navez et. al., Compt. Rend. Acad. Sci., 254, 240 (1962)
2/23/2019 7
60o
45o
10o

8. Observations (Nonconventional ways)
Ozaydyn Appl. Phys. Lett. (2005)
10o 30o
70o 80o
F. Frost et.al., Phys. Rev. Lett., 85, 4117 (2000)
2/23/2019 8
1000 eV Ar+  Si500 eV Ar+  InP
Sample rotation at oblique incidence
(Mo seeded)

9. Ion beam induced patterns over Si and Ge
Frost Appl. Phys. A 91, 551 (2008)
Important experimental parameters
• Ion beam energy
• Angle of incidence (0
o
-85
o
)
• Erosion time
• Ion species used Ar, Xe, Kr, Ne,O2,N2
• Temperature
• Rotation of sample/swing of sample
2/23/2019 9
Ge
Ge
Ge Ge

10. Temporal evolution of ripple: Simulation
Youtube (J. M. Garcia)
2/23/2019 10

11. Theoretical background
Monoelemental system
• Competition between two processes
• Roughening due to sputtering
• Smoothening due to diffusion
Bradley et al. J. Vac. Sci. Technol. A 6, 2390 (1988)
𝝏𝒉
𝝏𝒕
= −𝒗 𝟎 + 𝜸 𝜽
𝝏𝒉
𝝏𝒙
+ 𝝂 𝒙
𝝏 𝟐
𝒉
𝝏𝒙 𝟐
+ 𝝂 𝒚
𝝏 𝟐
𝒉
𝝏𝒚 𝟐
− 𝑲𝜵 𝟒
𝒉
Sputter
roughening
Diffusion
smoothing
Local slope
erosion
𝝏𝒉
𝝏𝒕
= −𝒗 𝟎 + 𝝊𝜵 𝟒
𝒉 − 𝑫𝜵 𝟒
𝒉 +
𝝀 𝟎
𝟐
𝜵𝒉 𝟐
Nonlinear terms (Kuramoto-Sivashinsky KS eq.)
𝝀 = 𝟐𝝅 𝟐𝑫
𝝊
2/23/2019 11
Bradley-Harper theory

12. Ion beam induced patterns over III-V semiconductor
Xu JAP 2004
Kumar ASS 2012
Roy PRB 10
500 eV Ar
 GaSb
50 keV Ar
 GaAs
500 eV Ar
 GaSb
Park SCT 2007
Mohanty ASS 2012
Atwani SR 2015
225 eV Ar
 InP
100 keV Ar
 InP
5 keV Xe
 GaP
Atwani APL 2012
Chowdhury ASS 2016
Paramanik JPDAP 2008
1 keV Ar
 GaAs
1 keV Ar
 GaSb
3 keV Ar
 InP
2/23/2019 12

13. Theory for binary compound
13
Shenoy et.al., Phys. Rev. Lett., 98, 256101 (2007)
A
B
AB binary compound
Coupled equation (50-50) composition
Sputtering yields (Y) and diffusivities (D) are different
𝝏𝒉
𝝏𝒕
= −𝜴[ 𝑭 𝑨 + 𝜵. 𝑱 𝑨 + (𝑭 𝑩 + 𝜵. 𝑱 𝑩)]
∆
𝝏𝒄 𝒔
𝝏𝒕
= 𝜴 𝒄 𝒃 − 𝟏 𝑭 𝑨 + 𝜵. 𝑱 𝑨 + 𝒄 𝒃 𝑭 𝑩 + 𝜵. 𝑱 𝑩
• Height modulation
• Composition modulation
2/23/2019 13
𝐹𝐴 = 𝐹𝑌𝐴 𝑐 𝑠
𝐹𝐵 = 𝐹𝑌𝐵(1 − 𝑐 𝑠)
𝐹 𝐴
𝐹 𝐵
=
𝑐 𝑏
1−𝑐 𝑏
Sign of 𝐷 𝐵 𝑌𝐴 − 𝐷𝐴 𝑌𝐵
decides the peaks and valleys
𝑐 𝑠=
𝑌𝐵 𝑐 𝑏
𝑌𝐴(1 − 𝑐 𝑏) + 𝑌𝐵 𝑐 𝑏
If 𝐷𝐴 𝑌𝐵 < 𝐷 𝐵 𝑌𝐴 peaks will be enriched with A
Differential sputtering yield and diffusivity

14. Impurity assisted ion beam nanopatterning
Khanbabaee TSF 2013
Fe, Kr
Macko NT 2010
Fe, Kr
Garcia JPCM 2009
2×2 μm2 Fe/Mo, Ar
2/23/2019 14
Diverse patterns -varying the ion beam parameters
• Flux of impurity atoms and ions
• Ion/impurity ratio is important
• Varies from place to place from on the substrate
• Different types impurity addition mechanisms
• Surfactant sputtering, from the clamps, chamber walls
Nanoholes Nanodots Discontinuous ripples
625×625 nm2

15. Motivation
• The atoms having energies∼50 eV essentially are a
part of the surface or near-surface layer having a
penetration depth of sub-nanometer dimension
• Mixtures containing initially well-mixed species
• Far from strongest coupling (50-50) composition
• Sputtering can induce stoichiometric
rearrangements in the bulk which affects the
surface concentration
CoxSi1-x is chosen as the binary material
2/23/2019 15
50 eV Ar  Si
50 eV Ar  Si

16. Experimental details
2/23/2019 16
CoxSi1-x deposition (Confocal magnetron sputtering)
Magnetic flux is shunted
No deposition
Modification of sputtering gun
Weak magnetic
material
Central magnet
replaced

17. Experimental details
• CoSi binary material deposited on Si(100) with variable
stoichiometries (SEM-EDX)
• Irradiated with different energies, fluence, angles and swinging
parameters
• Initial roughness ~ 5 nm
Si(100)
CoxSi1-x
After Ar ion irradiation
at 1200 eV
Unirradiated CoxSi1-x
2/23/2019 17

18. Energy variation
500-1200 eV
Morphology transitions from lower to higher value of energy
Ar+ Co27Si73 67o
7.5×1018 ions/cm2
0
20
40
600
800
1000
Wavelength(nm)
600 800 1000 1200
1
2
3
4
5
Amplitude(nm)
Energy (eV)
600 800 1000 1200
0.00
0.01
0.02
0.03
0.04
Aspectratio(A/L)
Energy (eV)
1
2
3
4
5
Roughness(nm)
As grown 5 nm
Parida et al. Curr. Appl. Phys. 18, 993 (2018 )
2/23/2019 18

19. Energy variation (Co27Si73)
10
6
10
7
10
8
1E-30
1E-29
1E-28
1E-27
1E-26
1E-25
500 eV
700 eV
10
5
10
6
10
7
1E-28
1E-27
1E-26
1E-25
1E-24
1E-23
PSD(m
3
)
k (m
-1
)
1000 eV
1200 eV
Calculations from KS equation
𝜕ℎ
𝜕𝑡
= −𝑣0 + 𝛾
𝜕ℎ
𝜕𝑥
+ 𝜈 𝑥
𝜕2ℎ
𝜕𝑥2
+ 𝜈 𝑦
𝜕2ℎ
𝜕𝑦2
+
𝜆 𝑥
2
𝜕ℎ
𝜕𝑥
2
+
𝜆 𝑦
2
𝜕ℎ
𝜕𝑦
2
− 𝐾𝛻4
ℎ − 𝐷𝛻4
ℎ+𝜂
Makeev et al. NIMB 197, 185 (2002)
In our case 𝜈 𝑥> 𝜈 𝑦 and 𝜈 𝑦 < 0 hence ripples are aligned along X-direction
2/23/2019 19
Ion induced surface diffusion is the dominant relaxation mechanism
Yi s sputtering yields, D=Diffusivity

20. Fluence variation (Co16Si84)
Wavelength increment follows power law
700 eV Ar+ Co16Si84 67o
(2.5 - 10)×1018 ions/cm2
Parida et al. Curr. Appl. Phys. 18, 993 (2018 )
2/23/2019 20

21. Compositional variations and MFM study
Topographical changes
Enrichment of cobalt at the peaks
Hierarchical (bug-like) structures
700 eV Ar+ CoxSi1-x 67o 7.5×1018 ions/cm2
Parida et al. Curr. Appl. Phys. 18, 993 (2018 )
2/23/2019 21

22. Silicide confirmation
Confirmation of Silicide formation
Parida et al. Curr. Appl. Phys. 18, 993 (2018 )
Phase diagram
2/23/2019 22
500 600 700 800 900 1000 1100 1200
0
5
10
15
20
25
50
51
52
53
54
55
Distorted Ripples
Pill bug structures
Semi-ellipsoidal structures
Self-organized ripples
Co(%)
Energy (eV)

23. -10 0 10 20 30 40 50 60 70 80 90
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Roughness(nm)
Angle of incidence (degree)
ion = Ar+
time =45 min
energy =700eV
Effect of angle of incidence variation (Ar ion)
θ=30o
θ=80oθ=67o
θ=0o
z=4 nm z=4.4 nm
z=74 nmz=23 nm
700 eV Ar+ Co43Si57
7.5×1018 ions/cm2
3D
10
-3
10
-2
10
-3
10
-2
10
-1
10
0
10
1
10
2
10
3
10
4
PSD(nm
4
)
Frequency(nm-1)
0 deg
30 deg
67 deg
80 deg
Nanodot formation at grazing incidence
Parida et al. Physica B 545, 34(2018 )
2/23/2019 23

24. Effect of angle of incidence variation (Xe ion)
Irregular dot structures to triangular structures
10
-3
10
-2
10
-2
10
-1
10
0
10
1
10
2
10
3
PSD(nm
4
)
Frequency(nm-1
)
0 deg
30 deg
50 deg
67 deg
-10 0 10 20 30 40 50 60 70
1.0
1.5
2.0
2.5
3.0
3.5
Roughness(nm)
Angle of incidence (degree)
ion = Xe+
time = 45 min
energy = 500 eV
Parida et al. Physica B 545, 34(2018 )
500 eV Xe+ Co64Si36
7.5×1018 ions/cm2
2/23/2019 24

25. Stoichiometric controlled nanopatterning
0.0 0.5 1.0 1.5 2.0
3.5
4.0
4.5
5.0
5.5
6.0
Roughness(nm)
Co/Si
Nanoripple
evolution
Within a specific composition ripples appear
Preparation
Ar 700 eV, 67o, 7.5×1018 ions/cm2
10
7
10
8
Co21.9
Si78.1
Co7.7
Si92.3
Co3.2
Si96.8
Co2.4
Si97.6
Co0
Si100
Co66.9
Si33.1
Co54
Si46
Co41
Si59
Co39.2
Si60.8
Co3.2
Si96.8
Co2.4
Si97.6
PSD(a.u)
k (m
-1
)
k
n
2/23/2019 25

26. Higher order ripples
0.00 0.25 0.50 0.75 1.00
-3.8
0.0
3.8
7.6
-1.7
0.0
1.7
3.4
-3.3
0.0
3.3
6.6
-1.5
0.0
1.5
3.0
-9
0
9
18
0.00 0.25 0.50 0.75 1.00
60 min
45 min
30 min
15 min
10 min
X (µm)
slope


Height(nm)
Line profiles
h
Higher order ripples
Shadowing causes hillocks
Communicated…
2/23/2019 26
500 eV Ar+ Co69Si31, 67o
10
7
10
8
10
9
10
-31
10
-30
10
-29
10
-28
10
-27
10
-26
10
-25
10
-24
PSD(m
3
)
k (m
-1
)
10 min
15 min
30 min
45 min
60 min
Along ion beam direction
10
7
10
8
10
9
10
-31
10
-30
10
-29
10
-28
10
-27
10
-26
10
-25
10
-24
10 min
15 min
30 min
45 min
60 min
Across ion beam direction
PSD(m
3
)
k (m
-1
)

27. Roughness and I-V characteristic study
Drastic change in electrical conductance as grown to patterned surface
Along and across the ion beam direction resistance is different
-20 -15 -10 -5 0 5 10 15 20
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
Current(A)
Voltage (V)
|| to the ion beam direction
to the ion beam direction
As-grown
Communicated…
2/23/2019 27
10 20 30 40 50 60
2
3
4
5
6
Roughness(nm)
Time (min)
10 20 30 40 50 60
33
36
39
42
45
48
51
54
57
(b)
Wavelength(nm)
Time (min)

28. I-V and resistance study
A trap state ~ ±5 V
Higher resistance for better ordered structures
10 20 30 40 50 60
200
400
600
800
1000
1200
1400
1600
1800
10 20 30 40 50 60
Amplitude(nm)
Time of irradiation (min)
|| to the ion beam direction
 to the ion beam direction
Amplitude
Resistance(ohm)
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
Communicated…
2/23/2019 28
I-V characteristic Resistance
-20 -15 -10 -5 0 5 10 15 20
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
-20 -15 -10 -5 0 5 10 15 20
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
15 min
30 min
60 min
45 min
10 min
Pristine
Current(A)
Voltage (V)
Parallel to the ion beam direction

29. Effect of azimuthal swinging
Kim et al. J. Phys.: Cond Matt 30, 274004 (2018) Yoon et al. J. Appl. Phys. 119, 205301 (2016)
Transition b/w erosive and diffusive region
Square-shaped vacancy islands
Ar+ 2 keV 78o, ∆φ=144o
Asymmetric wall like structure
Ar+ →HOPG
2 keV Ɵ=78o
∆φ=144o
2/23/2019 29

30. Pristine
-200o+200o
Z=50nm
-50o+50o -75o+75o
-150o+150o
-125o+125o -180o+180o
-100o+100o
(a) (b) (c) (d)
(e) (f) (g) (h)
Z=21nm Z=50nm Z=30nmZ=50nm(c)
-75o+75o
Z=45nmZ=35nmZ=24nm Z=40nm
Z
Constant parameters
500 eV, 67o,1.12×1018 ions/cm2 7 rpm speed in swinging
Effect of swinging on binary material
 Bi-periodic ion incidence on the swinging surface
 But single period for the rotating surface
 Anisotropic surface modification and the reduced symmetry in the pattern
 Lateral mass transport caused by the swinging substrate
Under preparation…
100 150 200 250 300 350 400
3.5
4.0
4.5
5.0
5.5
6.0
100 150 200 250 300 350 400
3.5
4.0
4.5
5.0
5.5
6.0Linear fit
Roughness(nm)
Angle of total swing (degree)
2/23/2019 30
Cauliflower like structures appear

31. Constant parameters 500 eV, 67o, 1.12×1018 ions/cm2 (-100o - +100o)
• Roughness decreases towards
higher speed swinging
Swinging speed variation
Under preparation…
2/23/2019 31
Z=40 nm
1 rpm
Z=30 nm
7 rpm
Z=30 nm
15 rpm
0 2 4 6 8 10 12 14 16
4.8
5.0
5.2
5.4
Roughness(nm)
Speed of swinging (rpm)
• Number density of Cauliflower
like structures grow up

32. 0 10 20 30 40 50 60 70 80 90 100
500
750
1000
1250
500
750
1000
1250
Energy(eV)
Perpendicularmoderipples
(16.7 keV)
~~
Si
~
~
~
~
~
~Ripples
Energy(eV)
Co atomic %
Co
Phase diagram before our work
2/23/2019 32
Ar+ →Co & Si

33. 0 10 20 30 40 50 60 70 80 90 100
500
750
1000
1250
500
750
1000
1250
Co69
Si31
Co27
Si73
*
Ellipsoidal
0
*Distorted Ripples
00
**
Anisotropiv I-V
~
~~
~ 0
0
0
0
Energy(eV)
Perpendicularmoderipples
(16.7 keV)
~~
Si
~
~
~
~
~
~Ripples
Energy(eV)
Co atomic %
Co
0
*
Phase diagram after our work
2/23/2019 33
Ar+ →Co, Si, CoxSi1-x

34. Summary
• Morphological transition at higher energies – nano to micro scale
• Power law behavior for fluence variations
• Hierarchical structures for higher Co concentrations
• Formation of conical bumps at grazing incident angles. Lower angles give
extremely smooth surfaces
• Higher resistance for better ordered structures
• Trap barrier ~ ± 5 V for nanorippled surface, amplitude dependent resistance
• Cauliflower like structures appear due to swinging
• Enrichment of cobalt at crests
2/23/2019 34

35. Publications
1. Morphological instabilities in argon ion sputtered CoSi binary mixture
B. K. Parida , M. Ranjan, S. Sarkar; Curr. Appl. Phys 18, 993 (2018)
2. Influence of obliquely incident primary ion species on patterning of CoSi binary
mixtures: An experimental study
B. K. Parida , M. Ranjan, S. Sarkar; Physica B 545, 34 (2018)
I. Anisotropic I-V behaviour from nanoripples of ion eroded CoSi surfaces
B. K. Parida , A. Kundu, K. S. Hazra, S. Sarkar (Communicated)
II. Stoichiometric controlled binary mixture nanopatterning via ion beam sputtering
B. K. Parida , S. Sarkar (Under Preparation)
III. Pattern formation assisted by ion beam sputtering over azimuthally oscillating CoSi
binary substrate
B. K. Parida , S. Sarkar (Under Preparation)
Supervisor - Dr. Subhendu Sarkar
Dr. Mukesh Ranjan, FCIPT, IPR, Gandhinagar
Dr. K. S. Hazra INST, Mohali
CRF, IIT Ropar
MHRD, India
Friends and Family
Acknowledgement
2/23/2019 35

36. 2/23/2019 36

37. 2/23/2019 37
Zhou thesis

38. 0 10 20 30 40 50 60 70
3.5
4.0
4.5
5.0
5.5
6.0
Roughness(nm)
Co% (a.u.)
3 µm
Nanoripple
evolution
0.0 0.5 1.0 1.5 2.0
0
4
8
12
16
20
24
28
32
0.0 0.5 1.0 1.5 2.0
Range(nm)
Co/Si
Range
Lateral range
Longitudinal range
Y Co
Y Si
Y Total
2.90
2.95
3.00
3.05
3.10
3.15
3.20
3.25
3.30
3.35
YTotal(atoms/ion)
(a) (b)
(d)
(c)
(g)
(f)(e)
(i)(h)
Z=30 nm
Z=22 nm
Z=40 nm
Z=35 nm
Z=40 nm
Z=26 nm
Z=30 nm
Z=28 nm
Z=30 nm
Z
Compositional effect
2/23/2019 38

39. 0 10 20 30 40 50 60 70 80 90
X
X
XXX
X XX
XXX
X
Perpendicularripples
Flat stable surface
0
~
~
~
1200
600
~
~
0
~400
800
200
1000
Paralel mode
Ripples
~
Energy(eV)
incidence angle (deg)
~ ~~
~
~
~
~
~
~
~ ~ ~
~~ ~ ~
X
X
X
XXX
Phase diagram before our work
2/23/2019 39
With Ar →Si

40. Phase diagram before our work
2/23/2019 40
0 10 20 30 40 50 60 70 80 90
0.0
0.4
0.8
1.2
16
18
20
0.0
0.4
0.8
1.2
16
18
20
Perpendicularmoderipples
No report
~
Energy(keV)
Incidence angle (deg)
~
With Ar →Co

41. 0 10 20 30 40 50 60 70
Anisotropic I-V
behavior
Co69
Si31
~~
Co22
Si78
Distorted ripples
0
Co16
Si84
~
Ellipsoidal
0
Co27
Si73
~
700
1000
500
1200
00
0
0
0
0
0
Ripples
~~
Energy(eV)
Co atomic %
700
1000
500
1200
Phase diagram of patterns formed
2/23/2019 41
With Ar→CoXSi1-x

42. 0 10 20 30 40 50 60 70 80 90 100
500
750
1000
1250
500
750
1000
1250
Energy(eV)
Perpendicularmoderipples
(16.7 keV)
~~
RipplesonSi
~
~
~
~
~
~Ripples
Energy(eV)
Co atomic %
Phase diagram after our work
2/23/2019 42
With Ar→CoXSi1-x

43. 0 10 20 30 40 50 60 70 80 90 100
Anisotropic I-V
behavior
Co69
Si31
~
Co22
Si78
Distorted ripples
0
Co16
Si84
~
Ellipsoidal
0
Co27
Si73
~
700
1000
500
1200
00
0
0
0
0
0
Ripples
~~
Energy(eV)
Co atomic %
700
1000
500
1200
Phase diagram after our work
2/23/2019 43
With Ar→CoXSi1-x

44. 0 10 20 30 40 50 60 70 80 90 100
Anisotropic I-V
behavior
Co69
Si31
~
Co22
Si78
Distorted ripples
0
Co16
Si84
~
Ellipsoidal
0
Co27
Si73
~
700
1000
500
1200
00
0
0
0
0
0
Ripples
~~
Energy(eV)
Co atomic %
700
1000
500
1200
Phase diagram after our work
2/23/2019 44
With Ar→CoXSi1-x

45. I-V characteristic study
-20 -15 -10 -5 0 5 10 15 20
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
-20 -15 -10 -5 0 5 10 15 20
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
15 min
30 min
60 min
45 min
10 min
Pristine
Current(A)
Voltage (V)
Parallel to the ion beam direction
Higher resistance for better ordered structures
A trap state ~ ±5 V
60 min
0.0 0.2 0.4 0.6 0.8 1.0
-10
0
10
20
0.0 0.2 0.4 0.6 0.8 1.0
-10
0
10
20
slope
Height(nm)
X (µm)



Shadowing
10 20 30 40 50 60
200
400
600
800
1000
1200
1400
1600
1800
10 20 30 40 50 60
Amplitude(nm)
Time of irradiation (min)
|| to the ion beam direction
 to the ion beam direction
AmplitudeResistance(ohm)
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
Communicated…
2/23/2019 45

46. Ion beam nanopatterning
Advantages
• Single step process for large area nanopatterning
• Faster and cheaper compared to conventional lithographic techniques
• Easily tunable process parameters
• High spatial selectivity
• Any ion beam can be put into any matter
• Maskless process
• Nanoripples and dots
Ion source
Sample holder
2/23/2019 46
Applications of these nanopatterns
• Quantum dots in optoeletronic devices
• Nanoripples for optical interference grating
• Ripple for alignment of carbon nanotubes
• Templates for functionalized surfaces e.g. plasmonic application

47. 2/23/2019 47
plasma
N S N
Target
substrate
fluxflux flux
N S N
Ferromagnetic target
substrate
fluxflux flux

48. Impurity assisted ion beam nanopatterning
Hofsass APA 2008
1×1 μm2
Vayalil JAP 2015
Ozadyn APL 2005
Mo, Ar
Khanbabaee TSF 2013
Fe, Kr
Macko NJP 2012
Fe, Kr
Cornejo ASS 2011
Fe, Kr
Macko NT 2010
Fe, Kr
Garcia JPCM 2009
2×2 μm2
Fe/Mo, ArAu, Xe
Fe, Ar
Cubero NT 2016
Mo, Xe
Gago NT 2014
Mo, Fe, Ar
Engler NT 2014
Ag, Pd, Pb, Ir, Fe, C, Ar
2/23/2019 48

49. Theory (binary compound)
Shipman et.al., Phys. Rev. B 84, 085420 (2011)
2/23/2019 49

50. I-V characteristic study
5 10 15 20 25 30 35 40 45 50 55 60 65
300
600
900
1200
1500
1800
300
600
900
1200
1500
1800
Resistance(Ohm)
Time (min)
|| to the ion beam
 to the ion beam
(d)
-20 -15 -10 -5 0 5 10 15 20
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
-20 -15 -10 -5 0 5 10 15 20
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
15 min
30 min
60 min
45 min
10 min
Pristine
Current(A)
Voltage (V)
Parallel to the ion beam direction
Higher resistance for better ordered structures
10 min 45 min
30 min
60 min15 min
0.0 0.2 0.4 0.6 0.8 1.0
-10
0
10
20
0.0 0.2 0.4 0.6 0.8 1.0
-10
0
10
20
slope
Height(nm)
X (µm)



Shadowing
Ar+  Co69Si31 500 eV, 67o,1×1018 ions/cm2
Communicated
2/23/2019 50

51. 2/23/2019 51

52. Why CoSi is important
• Especially true when a metal film is deposited and annealed to high temperatures to form the
silicide, e.g., in the self-aligned-silicide, or “salicide,” process
• Difficult to apply when very thin layers are desired, because the films exhibit grooving at grain
boundaries and the continuous him breaks up into islands in an attempt to further reduce free
energy
• Cobalt disilicide films have aroused considerable interest in the semiconductor industry because
of their low resistivity, thermal stability and good epitaxial alignment with a Si substrate
• Sputter deposition of Co thin films is difficult as it is a ferromagnetic material
• The dc magnetic field transmitted through a ferromagnetic material from one side to another is called the
pass-through flux ~PTF!.
• Considerable portion of magnetic flux from the system is shunted by the target itself
• High purity and extremely low roughness, wide availability
• Polycrystallinity
• Alloys of cobalt and rare earth (RE) metals generally possess a strong magnetocrystalline anisotropy and
usually a high Curie temperature.
Zhang cobalt sputter target
Why Co is less sputtered
2/23/2019 52

53. Surfactant sputtering
S. Macko et. al., Nanotech.
21, 085301(2010)
2 keV Kr+  Si, 300 K
Metal
2/23/2019 53

54. Constant parameters Ar+ ion
500 eV, 67o, 1.12×1018 ions/cm2 7 rpm speed during Swinging
Effect of swinging on CoxSi1-x
-7
0
7
0 1000 2000 3000
-6
0
6
-18
-9
0
9
-5
0
5
-12
-6
0
6
-8
0
8
16
-7
0
7
14
0 1000 2000 3000
-8
0
8
16
A
Height(nm)
As-grown
d
-50
o
+50
o
-75
o
+75
o
-100
o
+100
o
cauli flower like
-125
o
+125
o
cauli flower like
-150
o
+150
o
-180
o
+180
o
X (nm)
-200
o
+200
o
Cauliflower like structures appear
80 120 160 200 240 280 320 360 400
3.5
4.0
4.5
5.0
5.5
6.0
80 120 160 200 240 280 320 360 400
3.5
4.0
4.5
5.0
5.5
6.0Linear fit
Roughness(nm)
Angle of total swing (degree)
-200o+200o
-50o+50o
-150o+150o-125o+125o -180o+180o
-100o+100o-75o+75o
(a) (b) (c) (d)
(h)(g)(f)(e)
As-grown
Z
Under preparation…
2/23/2019 54

55. Bradley-Harper theory(contd…)
𝝏𝒉
𝝏𝒕
= −𝒗 𝟎 + 𝜸(𝜽)
𝝏𝒉
𝝏𝒙
+ 𝝂 𝒙
𝝏 𝟐 𝒉
𝝏𝒙 𝟐 + 𝝂 𝒚
𝝏 𝟐 𝒉
𝝏𝒚 𝟐 − 𝑲𝜵 𝟒
𝒉
𝝀 = 𝟐𝝅
𝒌 = 𝟐𝝅
𝟐𝑲
𝝂(𝒙,𝒚)
~(𝒇𝑻)
𝟏
𝟐 𝒆
−∆𝑬
𝒌 𝑩 𝑻
5 keV Xe+  HOPG
Small : x< y<0
Large : y< x and y <0
Habenicht et. al., PRB, 60, R2200 (1999)
2/23/2019 55

56. Binary alloy systems (contd…)
• Height modulation
𝜕ℎ
𝜕𝑡
= −𝛺[ 𝐹𝐴 + 𝛻. 𝐽 𝐴 + (𝐹𝐵 + 𝛻. 𝐽 𝐵)]
• Composition modulation
∆
𝜕𝑐 𝑠
𝜕𝑡
= Ω 𝑐 𝑏 − 1 𝐹𝐴 + 𝛻. 𝐽 𝐴 + 𝑐 𝑏 𝐹𝐵 + 𝛻. 𝐽 𝐵
• Erosion rate
𝑣0 = Ω(𝐹𝐴 + 𝐹𝐵)𝑃0
• Surface atomic current
𝑱𝒊 = −𝑫𝒊 𝒏 𝒔 𝜵𝑐 𝑠 𝒊
+
𝑫𝒊 𝑐 𝑠 𝒊 𝒏𝜴𝜸
𝒌 𝑩 𝑻
𝜵𝜵 𝟐 𝐡 − 𝝁𝒊 𝜵𝒉 𝐢 = 𝐀, 𝐁
• Power deposited per unit area
𝑃 = 𝑃0 + 𝛼𝛻2 𝑢 + 𝛽(𝛻𝑢)2
Shipman, Bradley, Phys. Rev. B , 84, 085420 (2011)
2/23/2019 56

57. Binary mixture
Gago JPCM (2018)2/23/2019 57

58. Parida et al. Physica B 545, 34(2018 )
2/23/2019 58

59. Binary alloy systems
• Coupling between topography and altered composition
• For A-B (50-50) alloy sputtering yield and composition
• Preferential sputtering
𝐹𝐴 = 𝐹𝑌𝐴 𝑐 𝑠 , 𝐹𝐵 = 𝐹𝑌𝐵(1 − 𝑐 𝑠)
• For steady state bulk composition
𝐹 𝐴
𝐹 𝐵
=
𝑐 𝑏
1−𝑐 𝑏
𝑐 𝑠=
𝑌𝐵 𝑐 𝑏
𝑌𝐴(1 − 𝑐 𝑏) + 𝑌𝐵 𝑐 𝑏
• Normal incidence over a binary compound leads arrays of nanodots
Shenoy et.al., Phys. Rev. Lett., 98, 256101 (2007)
Preferential sputtering and diffusivity
2/23/2019 59

60. Nanopatterning using ion beam
Advantages
• Single step Faster and cheaper process for large area patterning
• Nanoripples, dots, holes etc.
• Easy to tune the parameters(ion energy, angle, flux,)
Applications
• Quantum dots in optoeletronic devices
• Nanoripples for optical interference grating, plasmonic applications
• Templates for functionalized surfaces
S. Facsko et.al., Science, 285, 1551
(1999)
CoSi
500 eV, 67o,45 min
GaSb
500 eV, 0o,400Sec
Ar ion flux IPR
Our Work
2/23/2019 60

61. Binary alloy sputtering(contd…)
• Power deposited per unit area
𝑃 = 𝑃0 + 𝛼𝛻2
𝑢 + 𝛽(𝛻𝑢)2
• Mass conservation
𝜕ℎ
𝜕𝑡
= −Ω[ 𝐹𝐴 + 𝛻. 𝐽 𝐴 + (𝐹𝐵 + 𝛻. 𝐽 𝐵)]
• Rate of change of surface concentration
∆
𝜕𝑐 𝑠
𝜕𝑡
= Ω 𝑐 𝑏 − 1 𝐹𝐴 + 𝛻. 𝐽 𝐴 + 𝑐 𝑏 𝐹𝐵 + 𝛻. 𝐽 𝐵
• Erosion rate
𝑣0 = Ω(𝐹𝐴 + 𝐹𝐵)𝑃0
• Surface atomic current
𝑱𝒊 = −𝑫𝒊 𝒏 𝒔 𝜵𝑐 𝑠 𝒊
+
𝑫𝒊 𝑐 𝑠 𝒊
𝒏𝜴𝜸
𝒌 𝑩 𝑻
𝜵𝜵 𝟐
𝐡 − 𝝁𝒊 𝜵𝒉 , 𝐢 = 𝐀, 𝐁
• Instability
𝛼 𝐹𝐴 + 𝐹𝐵 > 𝜇 𝐴 + 𝜇 𝐵
Shipman ,Bradley Phys. Rev. B ,84,085420(2011)
2/23/2019 61

62. Beyond BH model (contd…)
• Nanodots
• Normal incidence – sample fixed
• Oblique incidence – sample rotation
• Instability due to local curvature
• Erosion rate < addition rate to surface
• Coarsening due to nonlinear terms
Surface
tension
Surface diffusion Lateral
growth
White
noise
Nonlinear Kuramoto-Sivashinsky equation
𝝏𝒉
𝝏𝒕
= −𝜈𝛻2ℎ − 𝐾𝛻4ℎ − 𝐷𝛻4ℎ + 𝛾1 𝛻ℎ 2 + 𝛾2 𝛻2 𝛻ℎ 2 + 𝜂
Coarsening
term
2/23/2019 62

63. Binary alloy systems (contd…)
• Height modulation
𝜕ℎ
𝜕𝑡
= −Ω[ 𝐹𝐴 + 𝛻. 𝐽 𝐴 + (𝐹𝐵 + 𝛻. 𝐽 𝐵)]
• Composition modulation
∆
𝜕𝑐 𝑠
𝜕𝑡
= Ω 𝑐 𝑏 − 1 𝐹𝐴 + 𝛻. 𝐽 𝐴 + 𝑐 𝑏 𝐹𝐵 + 𝛻. 𝐽 𝐵
• Erosion rate
𝑣0 = Ω(𝐹𝐴 + 𝐹𝐵)𝑃0
• Surface atomic current
𝑱𝒊 = −𝑫𝒊 𝒏 𝒔 𝜵𝑐 𝑠 𝒊
+
𝑫𝒊 𝑐 𝑠 𝒊 𝒏𝜴𝜸
𝒌 𝑩 𝑻
𝜵𝜵 𝟐 𝐡 − 𝝁𝒊 𝜵𝒉 , 𝐢 = 𝐀, 𝐁
• Power deposited per unit area
𝑃 = 𝑃0 + 𝛼𝛻2 𝑢 + 𝛽(𝛻𝑢)2
Shipman, Bradley, Phys. Rev. B , 84, 085420 (2011)
2/23/2019 63

64. I-V characteristic study
Manuscript submitted…
 Diode like behaviour for patterned surfaces
 Macro roughness effect dominates for higher fluence
 Resistance -more along parallel direction
 Amplitude of nanoripples play measure role for conductivity
10 20 30 40 50 60
200
400
600
800
1000
1200
1400
1600
1800
10 20 30 40 50 60
Amplitude(nm)
Time of irradiation (min)
|| to the ion beam direction
 to the ion beam direction
Amplitude
Resistance(ohm)
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2/23/2019 64

65. Ion beam nanopatterning
Ion source
Sample holder
• Single step process for large area
nanopatterning (upto few cm2 area)
• Faster and cheaper compared to
conventional lithographic techniques
Before irradiation
Ar+ 500 eV, 67o,15 min→Si
After irradiation
2/23/2019 65

66. Nanopatterns on elementary and binary compounds
Binary compound
• Nanoripple • Nanodots
https://www.hzdr.de/db/Cms?pOid=24344&pNid=2707
S. Facsko et.al., Science, 285, 1551 (1999)
Frost et.al. Phys. Rev. Lett. 85, 4116 (2000)
Ar→Si
500 eV, 30 min, 67o
Oblique Incidence
Normal Incidence
Oblique Incidence with
rotation
Ar→InP
500 eV, 2 min, 10o
Monoelemental
Without impurity With impurity to
elemental surface
Ar→GaSb
500 eV, 30 min, 0o
2/23/2019 66

67. • Differential sputtering yield and Differential
diffusivity
• Results altered topography and
composition
A
B
Theoretical background
𝝏𝒉
𝝏𝒕
= −𝒗 𝟎 + 𝜸 𝜽
𝝏𝒉
𝝏𝒙
+ 𝝂 𝒙
𝝏 𝟐
𝒉
𝝏𝒙 𝟐
+ 𝝂 𝒚
𝝏 𝟐
𝒉
𝝏𝒚 𝟐
− 𝑲𝜵 𝟒
𝒉 + ⋯ .
Sputter
roughening
Diffusion
smoothing
Bradley-Harper Model
Monoelemental system
Shenoy et.al., Phys. Rev. Lett., 98, 256101 (2007)
• Competition between two processes
• Roughening due to sputtering
• Smoothening due to diffusion
AB compound
𝜕ℎ
𝜕𝑡
= −Ω[ 𝐹𝐴 + 𝛻. 𝐽 𝐴 + (𝐹𝐵 + 𝛻. 𝐽 𝐵)]
∆
𝜕𝑐 𝑠
𝜕𝑡
= 𝛺 𝑐 𝑏 − 1 𝐹𝐴 + 𝛻. 𝐽 𝐴 + 𝑐 𝑏 𝐹𝐵 + 𝛻. 𝐽 𝐵
Binary compound system
Bradley et al. J. Vac. Sci. Technol. A 6, 2390 (1988)
2/23/2019 67