Low energy ion beam nanopatterning of CoxSi1-x Surfaces -Thesis Defense seminar

Department of Physics
Indian Institute of Technology Ropar
India-140001
Low energy ion beam
nanopatterning of
CoxSi1-x Surfaces
Basanta Kumar Parida
Defense Seminar

Chapters
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1. Introduction to ion beam nanopatterning
2. Experimental aspects
3. Morphological instabilities with energy and fluence
4. Influence of ion species and incidence angle
5. Anisotropic electrical conduction behavior
6. Effect of initial stoichiometry in pattern evolution
7. Effect of substrate swinging on morphology evolution
8. Summary and future possibilities
Basanta Kumar Parida, Defense seminar

6/28/2020 3
1
Introduction to ion beam nanopatterning

Ion beam nanopatterning
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Nanopatterning – to pattern materials on nanometer scale.
Nanopatterning
Top-
down
Bottom-
up
Lithographic
Self-organizing
Ion beam
nanopatterning
E-beam, UV
Advantages
• Single step fast process for
large area, self-organized
patterns
• Easy and independent tunable
parameters (E, F, θ, T…)
• Any ion beam can be put into
any matter (metal,
semiconductor, insulator)
• Maskless process -Nanoripples
and dots
Facsko et.al.
Science. 285, 1551 (1999)
Navez et. al.
Compt. Rend. Acad. Sci. 254, 240 (1962)

Observations (Nonconventional ways)
F. Frost et.al., Phys. Rev. Lett., 85, 4117 (2000)
6/28/2020 5
500 eV Ar+  InP rotation at oblique incidence
Applications of patterns (Magnetic, Plasmonics, Biological, …)
M. O. Liedke et.al.,
Phys. Rev. B. 87, 024424 (2013)
M Arya et.al.,
J. Phys. D: Appl. Phys. 50, 455603 (2017)
Teshome et al.,
Nanoscale 6, 1790 (2014)

Temporal evolution of ripples: Simulation
6/28/2020 6
Garcia et al., Phys. Rev. Lett. 98, 086101 (2006)
Wavelength ∝ t
RMS roughness ∝ t

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 + 𝝊𝜵 𝟐
𝒉 − 𝑫𝜵 𝟒
𝒉 +
𝝀 𝟎
𝟐
𝜵𝒉 𝟐
Nonlinear terms (Kuramoto-Sivashinsky eqn.)
𝝀 = 𝟐𝝅 𝟐𝑫
𝝊
6/28/2020 7
Bradley-Harper theory (1988)
if 𝜽 > 𝜽 𝒄
Nanopattern
appears
𝜽 𝜽
Collision cascade
Diffusion
𝝏𝒉
𝝏𝒕
= −𝒗 𝟎 + 𝜸 𝜽
𝝏𝒉
𝝏𝒙
+ 𝝂 𝒙
𝝏 𝟐
𝒉
𝝏𝒙 𝟐
+ 𝝂 𝒚
𝝏 𝟐
𝒉
𝝏𝒚 𝟐
− 𝑫𝜵 𝟒
𝒉
Sputter
roughening
Diffusion
smoothing
Local slope
erosion
Sputtering Diffusion

Theory for binary compound
Shenoy et.al. Phys. Rev. Lett., 98, 256101 (2007)
A
B
AB binary compoundCoupled equation for (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
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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
𝑌𝐵
𝑌𝐴 𝑌𝐴 ≠ 𝑌𝐵
Coupled equation
Binary
Monoelemental

Ion beam irradiated patterns on different surfaces
Frost et al. Appl. Phys. (2008)
Monoelemental
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Chan et al. J. Appl. Phys. (2007)
2000 eV Ar+ → Au
Semiconductors Metals
800 eV Ar+ → Cu
Roy et al. Phys. Rev. B (2010)
500 eV Ar  GaSb
Park et al. Surf. Coat. Tech (2007)
225 eV Ar +  InP
Binary compound
III-V sc
500 eV Ar+ → Si
Kim et. al. Phys. Rev. B. (2009)
Impurity free patterning
Impurity assisted
patterning
Khanbabaee Thin Solid Films (2013)
Fe, Kr
Hofsass et al. Appl. Phys. A (2008)

Motivation
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Single
element
Binary
compound
Ion beam
nanopatterning
Impurity
assisted
Pure binary
50-50 %
Region
of
interest
0-100 %
100-0 %
Engler et al. Nanotechnol. (2014)
Keller et al. Materials (2010)
Tan et al. JVSTA (2006)
A-B
Nanoripples
Nanodots
Flat Nanoripples Ripples+dots

Motivation
• Binary mixtures contain initially well-mixed species
• Mixing and diffusion are no more surface phenomena
• Ion irradiation induces stoichiometric rearrangements in the
bulk which affects the surface concentration
CoxSi1-x is chosen as the binary material
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50 eV, 67o Co  Si
500 eV, 67o Ar  Si
• The impurity atoms having energies ∼50 eV essentially
stay on the surface or near-surface layer having a
penetration depth of sub-nanometer dimension
• Why Co? Diffusivity of Co in Si is ~100 times than that of Si in Co
• For incident primary ion
species the depth is more
than impurity case
Mobility of elements due to ion irradiation
Elemental (only one)
Binary (two)
Sputter yield
Diffusivity

Phase diagram from literature survey
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Ar+ →Co, Si
0 10 20 30 40 50 60 70 80 90 100
500
750
1000
1250
500
750
1000
1250Ref.1-3
Ref. 5,6
Ref. 4
IImoderipples

Si
Energy(eV)
^moderipples
(16.7 keV)
~~
At higher energies also
~
~
~
~
~
~Ripples
Energy(eV)
Co atomic %
Co


References
1-Garcia et al. Mat. Sci. Eng. R (2014) 4-Ghose J. Phys.: Cond. Matt. (2009)
2-Chan et al. J. Appl. Phys. (2007) 5-Colino et al. Appl. Surf. Sci. (2011)
3-Keller et al. Materials (2010) 6-Arranz et al. J. Phys.: Conf. Ser (2010)

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2
Instrumentation and experimental

Experimental details
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CoxSi1-x deposition (Confocal magnetron sputtering)
Weak magnetic
material
Magnetron
Sputtering
chamber
Ion
source
chamber
Si-RF, Co-DC sputtering

- + + - +-AC CT CT AC
Ie
Id
Screen
grid
Cathode
Anode
Accelerator grid
Decelerator grid
Cathode
module
Discharge
module
Beam
module
Accelerator
module
Neutralizer
module
Ground to cabinet
Vacuum chamber
Ion source
Operating cables
Ion source chamber
Gas
ions
Tiltable holder
Kaufman ion source
Neutralizer
0o
85o
4 cm diameter
Broad beam ion source
6/28/2020 Basanta Kumar Parida, Defense seminar 15

Characterization methods
• Scanning electron microscopy (SEM)
• X-Ray diffraction
• Atomic Force Microscopy
– RMS roughness(Rq) for height fluctuations
– Power spectral density (PSD), Fast Fourier transform (FFT), Auto-correlation
function (for periodicity, wavelength, lateral ordering, etc)
– Magnetic force microscopy (for magnetic phase)
• Current-voltage (I-V) measurement
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𝑅 𝑞 =
1
𝑛
𝑖=1
𝑛
(ℎ𝑖 − ℎ)2
Source-Google
Ziberi et al. Vacuum 81, 155 (2006)

Experimental details
• CoSi binary material deposited on Si(100) with variable stoichiometries
(SEM-EDX) - Si-RF, Co-DC sputtering
• Irradiated with different energies (eV), fluence (ions/cm2), angles of
incidence (degree) and swinging parameters (swinging angle and
speed), Base pressure- 1.0×10-7 Torr, Working Pressure-1.0×10-4 Torr
• Initial roughness ~ 5 nm
6/28/2020 17Basanta Kumar Parida, Defense seminar
200 nm

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3Morphological instabilities with energy and fluence
Ar→E,F

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
Energy variation
500-1200 eV
Morphology transitions from lower to higher value of energy
Ar+ Co27Si73, 67o
7.5×1018 ions/cm2
Parida et al. Curr. Appl. Phys. 18, 993 (2018)
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Arrow (ion beam direction)
0
20
40
600
800
1000
Wavelength(nm)
600 800 1000 1200
1
2
3
4
5
Amplitude(nm)
Energy (eV)

Energy variation
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
− 𝐷𝛻4ℎ+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
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Ion induced surface diffusion is the dominant relaxation mechanism
Yi s sputtering yields, D=Diffusion related term
IISD-Ion induced surface diffusion
T D -Thermal diffusion

Fluence variation
Wavelength increment follows power law
700 eV Ar+ Co16Si84 67o
(2.5 - 10)×1018 ions/cm2
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Arrows represent ion beam direction

Silicide confirmation and MFM study
Topographical changes
Enrichment of cobalt at the peaks
XRD after irradiation
Ar+, 700 eV,67o
7.5×1018 ions/cm2
Ar+, 700 eV,67o
Ar+, 67o,7.5×1018 ions/cm2

6/28/2020 23
4Influence of ion species and incidence angle
Ar, Xe→𝜽,s

-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 )

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

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5
Anisotropic electrical conduction behavior
B. K. Parida, A. Kundu, K. S. Hazra, S. Sarkar (Submitted)

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
Manuscript submitted
6/28/2020 27
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
Shadowing condition
tan(
𝜋
2
− 𝜃) ≥ 2𝜋ℎ/Λ

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
6/28/2020 28
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)

I-V and resistance study
Absence of electrical conductance in ~ ±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
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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

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6
Effect of stoichiometry in pattern evolution
B. K. Parida, S. Sarkar (Under review )

Ripples appear within a narrow window of stoichiometric variation
Ar 700 eV, 67o, 7.5×1018 ions/cm2
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10
7
10
8
Co22
Si78
Co8
Si92
Co3
Si97
Co2
Si98
Co0
Si100
Co67
Si33
Co54
Si46
Co41
Si59
Co39
Si61
PSD(a.u)
k (m
-1
)
k
n
Manuscript under review

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)
0 10 20 30 40 50 60 70
3.5
4.0
4.5
5.0
5.5
6.0
3.5
4.0
4.5
5.0
5.5
6.0
Roughness(nm)
Cobalt (atomic %)
Nanoripple evolution
100 90 80 70 60 50 40 30
Silicon (atomic %)
Ripple formation region
Manuscript under review
0.0 0.5 1.0 1.5 2.0
20
30
40
50
60
70
20
30
40
50
60
70
0 30 60 90 120 150 180
x
self-correlation(a.u)
x (nm)
x
y
2Lx
Lx
(nm)
Co/Si
(a)0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0.0 0.5 1.0 1.5 2.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
(b)
x
y
x
y

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7
Effect of swinging on morphology evolution
B. K. Parida, S. Sarkar (Under preparation)

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

Constant parameters
500 eV, 67o, 1.12×1018 ions/cm2, 7 rpm speed of swinging
Effect of swinging on binary material
 Anisotropic surface modification reduces symmetry in the pattern
 Lateral mass transport caused by the swinging substrate
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)
6/28/2020 35
Cauliflower like structures appear
Under preparation…

Constant parameters 500 eV, 67o, 1.12×1018 ions/cm2 (-100o - +100o)
• Roughness decreases towards
higher speed swinging
Swinging speed variation
Under preparation…
6/28/2020 36
Z=40 nm
1 rpm
Z=30 nm
7 rpm
Z=30 nm
15 rpm
0 2 4 6 8 10 12 14 16
4.2
4.4
4.6
4.8
Roughness(nm)
Speed of swinging (rpm)
• Number density of cauliflower
like structures grows up

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8
Summary and future possibilities

Phase diagram before our work
6/28/2020 38
Ar+ →Co, Si
0 10 20 30 40 50 60 70 80 90 100
500
750
1000
1250
500
750
1000
1250Ref.1-3
Ref. 5,6
Ref. 4
IImoderipples

Si
Energy(eV)
^moderipples
(16.7 keV)
~~
~
~
~
~
~
~Ripples
Energy(eV)
Co atomic %
Co


References
1-Garcia et al. Mat. Sci. Eng. R (2014) 4-Ghose J. Phys.: Cond. Matt. (2009)
2-Chan et al. J. Appl. Phys. (2007) 5-Colino et al. Appl. Surf. Sci. (2011)
3-Keller et al. Materials (2010) 6-Arranz et al. J. Phys.: Conf. Ser (2010)

Phase diagram after our work
6/28/2020 39
Ar+ →Co, Si, CoxSi1-x
0 10 20 30 40 50 60 70 80 90 100
500
750
1000
1250
500
750
1000
1250
Ref. 7, 8, 9-11
Ref. 1-3
Ref. 5,6
Ref. 4 
IImoderipples

Si
Co69Si31
Co27Si73
*
Ellipsoidal
0
*Distorted Ripples
00
**
Anisotropic I-V
~
~~
~ 0
0
0
0
Energy(eV)
^moderipples
(16.7 keV)
~~
~
~
~
~
~
~Ripples
Energy(eV)
Co atomic %
Co
0
*


References
1-Garcia et al. Mat. Sci. Eng. R (2014) 4-Ghose J. Phys.: Cond. Matt. (2009) 7-Parida et al. Curr. Appl. Phys. (2018)
2-Chan et al. J. Appl. Phys. (2007) 5-Colino et al. Appl. Surf. Sci. (2011) 8-Parida et al. Physica B (2018)
3-Keller et al. Materials (2010) 6-Arranz et al. J. Phys.: Conf. Ser (2010) 9-11-Parida et al. Submitted

Summary
• Incident energy variation can provide nm to µm size structures. Higher momentum
transfer disrupts nanostructuring
• Surface roughness and amplitude increase are monotonic with energy
• Ripple wavelength follows a power law with fluence. Gives well ordered ripples at early
times and shadowing effects for larger time scales
• Stoichiometric variation shows drastic morphology transitions (ripples, bugs etc.). Ripples
are best formed for 40-60 ratio of Co-Si and not for 50-50 as found in theoretical studies
• Peak enrichment occurs for Co under bombardment
• Silicide formation takes place for high fluence, high energy and low Co concentration
• Dot formation occurs at grazing incidence. Normal incidence causes smoothening
• Anisotropic electrical conduction shows trap barrier and depends on ripple orientation
• Sample swinging has increasing effect on roughness. Swing speed however decreases
surface roughness

Future outlook
• Mobility (diffusivity) of constituent atoms needs further study with respect to
bombardment parameters
• Role of silicide formation leading to nanostructuring needs further attention.
Conflicting studies found in literature
• A complete theoretical understanding of ion beam nanostructuring for a full
stoichiometric range is still awaited
• Binary compounds can yield better ordered structures than elemental ones
(theory exists - no experimental proof yet !!)
• Magnetic and electrical studies on such surfaces can lead to interesting
practical applications

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 (Manuscript submitted)
II. Stoichiometric controlled binary mixture nanopatterning via ion beam
sputtering
B. K. Parida, S. Sarkar (Under review)
III. Pattern formation assisted by ion beam sputtering over azimuthally oscillating
CoSi binary substrate
B. K. Parida, S. Sarkar (Under Preparation)

Academic conferences
1. Poster presentation at 2nd CRIKC Nanoscience Day, INST Mohali, 8 Aug, 2016
2. Poster presentation at 3rd IUMRS International Conference of Young Researchers on
Advanced Materials, IISC Bangalore, 11-15 Dec 2016
3. Oral presentation at 4th International conference on nano-structuring by ion beam (ICNIB
2017) , DAVV Indore, 11-13 Oct 2017
4. Oral presentation at 5th International conference on ion beams in materials engineering
and characterizations, IUAC New Delhi, 09-12 Oct 2018
5. Oral presentation at 10th International Workshop on Nanoscale Pattern Formation at
Surfaces (NanoPatterning 2019), 07-10 July 2019 at the University of Surrey in Guildford, UK
6/28/2020 43
1. DST-SERB school on `ion interaction with solid’, Saurashtra University Rajkot, 2-22 March, 2015
2. National Program on Differential Equations: Theory, Computation and Applications (NPDE-
TCA) 2016 IIT Ropar, India.
3. Workshop on Scientific and Technical Writing organized by Department of
Humanities and Social Sciences IIT Ropar India on 28-29 Nov 2016
Scientific schools

Acknowledgement
6/28/2020 44
Supervisor- Dr. Subhendu Sarkar
DC Members- Dr. Mukesh Kumar, Dr. S. Dasgupta, Dr. R. Srivastava
External expert- Prof. Satyaranjan Bhattacharyya (SINP, Kolkata)
Foreign expert- Prof. Rodolfo Cuerno
Internal examiner- Dr. C. M. Nagaraja
Dr. Mukesh Ranjan, FCIPT, IPR, Gandhinagar
Mr. Subash Pai, Excel Inst. Mumbai
Central Research Facility, IIT Ropar
Department of Physics
MHRD and DST-SERB, India
Friends and Family

Thank you

Effect of dispersion on the nanoscale patterns
Loew and Bradley, Phys. Rev. E 100, 012801 (2019)
As-grown Experimental Theory
Irradiated
Protrusions and depressions are triangular in shape due to dispersion
More raised triangles than depressed
𝝏𝒉
𝝏𝒕
= −𝒗 𝟎 + 𝝊𝜵 𝟐 𝒉 − 𝑫𝜵 𝟒 𝒉 +
𝝀 𝟎
𝟐
𝜵𝒉 𝟐 + 𝑪 𝟏𝟏𝟏
𝝏 𝟑
𝒉
𝝏𝒙 𝟑
+ 𝑪 𝟏𝟐𝟐
𝝏 𝟑
𝒉
𝝏𝒙𝝏 𝟐 𝒚
unirradiated

Impurity types in IBS
Liu APA 2018
Hofsass APA 2013
Lloyd SS 2016
Zhang NJP 2011
Zhang NT 2014
Zhou JAP 2011
Engler NT 2014

Surface properties of swinging substrates
Sku<3: Height distribution is skewed above the mean plane.
Sku=3: normal. (Sharp portions and indented portions co-exist.)
Sku>3: is spiked.
100 150 200 250 300 350 400
0.15
0.30
0.45
0.60
0.75
0.90
1.05
1.20
100 150 200 250 300 350 400
0.0
0.5
1.0
1.5
2.0
2.5
Skewness
Total swinging angle
Kurtosis
Swinging angle (deg)
0 2 4 6 8 10 12 14 16
0.0
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
0 2 4 6 8 10 12 14 16
0.0
2.5
5.0
7.5
10.0
Skewness
Swinging speed
Kurtosis
Swinging speed (rpm)
Ssk<0: Height distribution is skewed above the mean plane.
Ssk=0: (peaks and pits) is symmetrical around the mean plane.
Ssk>0: is skewed below the mean plane.
Lower speed
swung surfaces
are more
peaky

Significance of KS equation terms
6/28/2020 49
Linear terms second order Nonlinear terms
Lateral growth

6/28/2020 50
Xu et al. JAP (2004)
Facsko et al. Science (1999)

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
6/28/2020 52
With Ar →Si

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
6/28/2020 53
With Ar→CoXSi1-x

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
6/28/2020 54
With Ar→CoXSi1-x

Ferromagnetic material sputtering
plasma
N
S
S
N
N
S
Target
substrate
fluxflux flux
N
S
S
N
N
S
Ferromagnetic target
substrate
fluxflux flux

Theory (binary compound)
Shipman et.al., Phys. Rev. B 84, 085420
(2011)6/28/2020 56Basanta Kumar Parida, Defense seminar

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)

Binary alloy systems (contd…)
𝜕ℎ
𝜕𝑡
= −𝛺[ 𝐹𝐴 + 𝛻. 𝐽 𝐴 + (𝐹𝐵 + 𝛻. 𝐽 𝐵)]
∆
𝜕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)

Binary alloy sputtering(contd…)
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
𝑱𝒊 = −𝑫𝒊 𝒏 𝒔 𝜵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)

Binary alloy systems (contd…)
𝜕ℎ
𝜕𝑡
= −Ω[ 𝐹𝐴 + 𝛻. 𝐽 𝐴 + (𝐹𝐵 + 𝛻. 𝐽 𝐵)]
∆
𝜕𝑐 𝑠
𝜕𝑡
= Ω 𝑐 𝑏 − 1 𝐹𝐴 + 𝛻. 𝐽 𝐴 + 𝑐 𝑏 𝐹𝐵 + 𝛻. 𝐽 𝐵
• Erosion rate
𝑱𝒊 = −𝑫𝒊 𝒏 𝒔 𝜵𝑐 𝑠 𝒊
+
𝒏𝜴𝜸
𝒌 𝑩 𝑻
𝜵𝜵 𝟐
𝐡 − 𝝁𝒊 𝜵𝒉 , 𝐢 = 𝐀, 𝐁
𝑃 = 𝑃0 + 𝛼𝛻2 𝑢 + 𝛽(𝛻𝑢)2
Shipman, Bradley, Phys. Rev. B , 84, 085420 (2011)

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