Lower sputtering yield of the discharge wall material is a crucial parameter for the performance of Hall Effect Thruster (HET) [1, 2]. In this article, we report the sputtering yield of HET wall material BNSiO2 (borosil) at elevated temperature ~600 °C using quartz crystal microbalance (QCM). We observe a linear increase in the sputtering yield with temperature and it remains stable during long duration experiments using Xe ions. Two different crystallographic orientations of borosil give a slight variation in the yield. The higher yields for higher operating temperatures is proposed to be due to the thermal spike nature. Microscopic surface morphology shows only different grains of BNSiO2, however high resolution nanoscopic view reveals the formation of nanoripple like structures over different grains [3]. The periodicity of such features increases with ion dose (sputtering time) and temperature in the range of 70-190 nm. Local curvature dependent erosion plays crucial role in such pattern formation [4]. Reference: 1. D.M. Goebel, I. Katz, Fundamentals of Electric Propulsion, Ion and Hall Thrusters, 2008. 2. M. Ranjan, A. Sharma, A. Vaid, T. Bhatt, V. Nandalan, M.G. James, H. Revathi, S. Mukherjee, AIP Adv. 6 (2016) 95224 3. R. M. Bradley, J.M.E. Harper, J. Vac. Sci. Technol. A 6 (1988) 2390 4. B. K. Parida, Sooraj K P, S. Hans, V. Pachchigar, S. Augustine, Remyamol T, M. R. Ajith, M. Ranjan; Nucl. Inst and Methods B, 514 (2022) 1-7

1. Sputtering yield and nanopattern formation study of BNSiO2
(Borosil) at elevated temperature relevance to Hall Effect
Thruster
By
Basanta Kumar Parida
Post Doctoral Fellow
FCIPT-IPR

2. 2
Outline of the talk
Ion beam nanopatterning
Sputtering yield related Hall Effect Thruster
Study on Borosil
Morphological changes and sputtering yield measurements
Conclusions

3. Ion solid interaction process
3
Jain et al. Surf. Sci. 66, 77 (2011)
 When an energetic ion passes through a
solid, it loses energy through elastic and
inelastic collison processes.
 The interaction of ions with any material is a
deciding factor in the ion beam material
modification..
 Nuclear and electronic energy losses
 Collision cascade-a disturbed region sue
to ion bombardment
 Sputtering yield=No of atoms ejected per
incident ions
 Helpful for surface modification-
nanostructuring
 Our primary interest is to understand the
role of ion sputtering in electric propulsion
(EP) thrusters used for satellite and space
exploration

4. Nanopatterning
4
Methods to create pattern on a nanometre scale
Before irradiation
Ar+ 500 eV, 67o,15 min
→Si
After irradiation
Ion beam nanopatterning
 Mask less process
 Self organized process
 Large area patterning
 Faster and cheaper than other
conventional lithographic process
 Easily tunable ion beam parameters
(Energy, time, angle, type of ion,
temperature, substrate rotation)
Norris et al., Appl. Phys. Rev. (2019)
FIB FIB

5. Ion beam induced nanopatterns over different semiconductors
Xu JAP 2004
Kumar ASS 2012
Roy PRB 10
500 eV Ar, 0 deg, 20 s
 GaSb
Nano islands
50 keV Ar,50deg,
15min
 GaAs
 Sparse nanodots
500 eV Ar, 45 deg,600s
 GaSb
tilted pillars
Park SCT 2007
Mohanty ASS 2012
Atwani SR 2015
180 eV Ar, 15min
 InP
Rotation
nanograss
100 keV Ar,30deg,
 InP
nanodots
5 keV Xe
 GaP
nanoripple
Atwani APL 2012
Chowdhury ASS 2016
Paramanik JPDAP 2008
1 keV Ar
 GaAs
nanoripple
1 keV Ar, 0deg, 15min
 GaSb
 nanodot
3 keV Ar, 0 deg 40 min
 InP
 nanodots
5
1.251.25 μmμm
0.50.5 μmμm
22 μmμm

6. Theoretical background
• 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
= −𝒗𝟎 + 𝜸 𝜽
𝝏𝒉
𝝏𝒙
+ 𝝂𝒙
𝝏𝟐
𝒉
𝝏𝒙𝟐
+ 𝝂𝒚
𝝏𝟐
𝒉
𝝏𝒚𝟐
− 𝑲𝜵𝟒
𝒉
Sputter
roughening
Diffusion
smoothing
Local slope
erosion
𝝏𝒉
𝝏𝒕
= −𝒗𝟎 + 𝝊𝜵𝟒
𝒉 − 𝑫𝜵𝟒
𝒉 +
𝝀𝟎
𝟐
𝜵𝒉 𝟐
Nonlinear terms (Kuramoto-Sivashinsky KS eq.)
𝝀 = 𝟐𝝅 𝟐𝑫
𝝊
6
Bradley-Harper theory (1988)
Collision cascade
Characteristic length

7. Thruster wall life and sputtering yield
7
 Hall Effect Thrusters (HET) are widely used in electric propulsion
system of satellites
 Plasma thrusters consist a narrow annular channel and with inner
ceramic wall (BN, BNSiO2 etc.)
 The ejected ions erode this ceramic at the ejection point edge.
 The eroded material may eventually deposit on the crucial parts of
the satellite and degrade their efficiency, mostly solar panels in
satellites
 So the erosion rate or the sputtering yield is a crucial thing to be
experimented (We focused on elevated temperature)
Zurbach et al. AIAA (2013) Conversano et al. IEEE (2015)
Yu et al. JPDAP (2006)

8.  Weight loss technique - complexity of the system, contamination issue
 Rutherford backscattering (RBS)- requires expensive accelerator beam lines
 Cavity ring-down spectroscopy (CRDS) - expensive technique with laser
 QCM is a cost effective and very sensitive method
Dr. Basanta Kumar Parida (Postdoc fellow-Institute for Plasma Research, Gandhinagar) 8
Why Quartz Crystal Microbalance is used?
o Most suitable for in-situ measurement for extremely low sputtering yield
measurements
o Sensing capability down to nanogram
o QCM measurements, not only capable of giving total sputter yield but also,
gives trajectories of the sputter material at a given angle and energy of
incidence

9. How QCM measures the sputtering yield?
9
QCM measures the sputtered mass accumulated on the sensor from the sample in a circular arc arc.
𝑌 α, φ =
∆𝑚 α, φ 𝑟𝑞𝑐𝑚
2
𝜌𝐽𝐵,𝑎𝑣𝑔 𝐴𝑠
𝑌 = Volumetric sputtering yield
∆𝑚=mass accumulation rate=(ng/cm2)
𝛼 =QCM angle
𝜑 =Azimuthal angle
𝜌=density of target material
𝐽𝐵, 𝑎𝑣𝑔=current density
𝐴𝑠=area of QCM sensor (0.535 cm2)
∆𝑚 =
𝐶𝑓
∆𝑓
𝐶𝑓 = the sensitivity factor for the crystal used
𝒀BNSiO2

10. Experimental set up
 Heater development was required for the high temperature experiments
10

11. UHV heater development
11
Temp is not upto the level
high current ~80 A
to get 400-500o C
Load lock arrangement
disturbed Ceramic based heater
I II III IV

12. Initial surface morphology BNSiO2
12
799.33 nm
0.00 nm
600nm
0 μm
Z=0.8 μm
2 μm
 Heterogeneous planar surface having random orientation of grains.
 The root-mean-square surface roughness of pristine surfaces is found to be in the range of ~ 70 nm

13. Morphology change with temperature variation
13
(c) 200 oC
RT
(a)
400 oC
(d)
100 oC
(b)
74{1/µm}
𝝀 ∝ 𝟐𝑫𝒆𝒙𝒑(−𝑬/𝟐𝒌𝑻)/𝝂
Ion beam parameters- Xe, 500 eV, 45 min, Angle-55o
200 nm
𝝀 = characteristic length of nanoripple.
𝐷 = diffusion constant,
𝐸 = activation energy for surface diffusion,
𝑘 = Boltzmann constant
𝑇 = absolute temperature
𝜈 =parameter proportional to ion flux and
penetration depth

14. Morphology change with irradiation time
14
15 min
74{1/µm}
30 min
74{1/µm}
45 min
74{1/µm}
60 min
74{1/µm}
0 100 200 300 400 500 600
0
10
20
30
40
50
Height
(nm)
Lateral length (nm)
Ion beam parameters- Xe, 500 eV, 45 min, Angle-55o
200 nm

15. Terrace formation
15
Harrison et al. Phys. Rev. E(2017)
 Surfaces exhibit interrupted coarsening- local slope variation
 The characteristic width and height of the surface disturbance grow for a time but ultimately asymptote to
finite values as the fully terraced state develops.
Pearson et al. JPCM (2015)
200 nm
200 nm
Higher order nonlinearity

16. Sputtering yield with temperature
16
0 100 200 300 400 500 600
0.6
0.8
1.0
1.2
1.4
1.6
1.8
BNSiO2
-IMP-ll-55
o
BNSiO2
-IMP-Lr-55
o
BNSiO2
-IMP-Cut-Lr-2-55
o
BNIn-1-55
o
BNSIN-(3)-55
o
BNSIN-14-55
o
Rate
(ng/cm
2
/s)
Temperature (
o
C)
BNSiN-(6)-55
o
BNSiN-(7)-55
o
BNSiN-(8)-55
o
BNSiO2
-IMP-55
o
BNSIN-(9)-55
o
BNSIN-(2)-55
o
0 100 200 300 400 500 600
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.26
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.26
Rubin et al.
Garnier et al.
BNSiO2
-ll
BNSiO2
-Lr
Sputtering
yield
(mm
3
C
-1
)
Temperature (
o
C)
Ranjan et al.
Parida et al. Nucl. Inst. and Methods B; 514 (2022) 1-7
Details of the erosion rate for all samples
 Yield increases due to thermal spike
 Momentum transfer from ion to the surface
 Damage annihilation increases the collision efficiency
 High-mass bombarding ions (Xe) favors the formation of clusters on the surface- increases the yield
Garnier et al. J. Vac. Sci. Technol. A 17 (1999) 3246.
Rubin et al.30th Int. Electr. Propuls. Conf., Florence, Italy (2007) 074
Ranjan et al. AIP Adv. 6 (2016) 095224

17. Yield study for long time irradiation
17
0 5 10 15 20 25 30 35 40 45 50 55 60 65
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.26
0 5 10 15 20 25 30 35 40 45 50 55 60 65
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.26
Sputtering
yield
(mm
3
C
-1
)
Sputtering Time (min)
BNSiO2
-ll
BNSiO2
-
Parida et al. Nucl. Inst. and Methods B; 514 (2022) 1-7
Yield remains stable even for long time of irradiation, which is
crucial for the thruster operation

18. Crystallographic and compositional change after irradiation
18
Sample BNSiO2
Element
Before
Irradiation
After 15 min
Irradiation
After 30 min
Irradiation
After 45 min
Irradiation
After 60 min
Irradiation
B 51.235 50.45 49.61 48.36 46.59
N 39.9 32.86 25.87 18.685 14.32
Si 2.175 5.4 7.82 9.42 10.85
O 6.69 11.29 16.7 22.955 28.24
 As the sample is irradiated for 15, 30, 45 and 60 min the B and N compositions decrease
and Si and O values increase.
 This indicates that B and N preferentially sputter faster and more and more Si and O remain
over the surface resulting in higher compositional concentrations.
EDX

19. 19
Conclusions
 Linear increase in the sputtering yield with temperature and remains stable during long
duration experiments using Xe ions.
 Two different crystallographic orientations of borosil give a slight variation in the yield
 Formation of nanoripple like structures over different grains.
 The periodicity of such features increases with ion dose (sputtering time) and
temperature in the range of 70–190 nm.
 Local curvature dependent erosion plays crucial role in such pattern formation.

20. Achievements
20
Dr. Basanta Kumar Parida (Postdoc fellow-Institute for Plasma Research, Gandhinagar)
Borosil (BNSiO2) material prepared by VSSC-ISRO and tested in our lab is approved for Indian satellite
Publications
1. B. K. Parida, Sooraj K P, S. Hans, V. Pachchigar, S. Augustine, Remyamol T, M R Ajith, M. Ranjan
Sputtering yield and nanopattern formation study of BNSiO2 (borosil) at elevated temperature relevance to Hall Effect Thruster, Nucl.
Inst. and Methods B; 514 (2022) 1-7 https://doi.org/10.1016/j.nimb.2022.01.001
2. S. Hans, B. K. Parida, V. Pachchigar, S. Augustine, M. Saini, K. P. Sooraj, M. Ranjan
Temperature influence on the formation of triangular features superimposed on nanoripples produced by low-energy ion beam.
Surfaces and Interfaces; 28 (2021) 101619 https://doi.org/10.1016/j.surfin.2021.101619
Conference presentation
Nanostructuring of BNSiO2 (borosil) Using Ion Beam
at Elevated Temperature, 6th International Virtual Conference on Nanostructuring by Ion Beams (ICNIB 2021) October 5-8, 2021

21. Acknowledgment
• Dr. Mukesh Ranjan (Supervisor)
• LPSC and PMI colleagues
• Other FCIPT colleagues
• Plasma Surface Engineering Division (FCIPT)
• Institute for Plasma Research, Gandhinagar
21
Thank you

22. 22

23. Previous study by the group
23
55o
 Sputtering yield increases with ion energy
 A maximum sputtering yield at 55o angle of incidence
 So in our experiments we kept this value as the reference for all studies.

24. Future plan Cu/Co/Si multilayer patterning and application
24
137.47 nm
0.00 nm
2.0µm
315.02 nm
0.00 nm
2.0µm

25. CuCo-400eV
25
244.86 nm
0.00 nm
400nm