Charging behavior of the calcite (100) surface investigated by KPFM
M. Mirkowska 1,2 , M. Kratzer 2 , C. Teichert 2 , H. Flachberger 1
1 Chair of Mineral Processing, Department of Mineral Resources and Petroleum Engineering, Montanuniversität Leoben, Leoben, Austria
2 Institute of Physics, Montanuniversität Leoben, Leoben, Austria
Experimental
Equipment:
Asylum Research MFP-3D AFM
Probes:
TiN coated tips for noncontact AFM,
spring constant ∼70 N/m, tip curvature radius ∼35 nm
Samples:
monocrystalline calcite, CaCO3 (100), MTI Corporation, USA
Conditions:
air, room temperature, 50 % r.H., applied forces: 2-3 µF, applied voltage: ±10 V
Measurement procedure:
sample
First pass Second pass
sample
h
Σ
VDC VAC
∼
KPFM measurements
Surface height Surface potential
KPFM charging KPFM
measurements (rubbing or static contact) measurements repeating
• Successful charging by static contact as well as by rubbing is confirmed by CPD change.
• The resulting surface charge depends on:
- the type of charging (static charging, rubbing), - the value of the initial surface potential.
• Charging can be reversed by application of opposite tip bias.
• Charge decays roughly exponentially with time.
Monika Mirkowska, e-mail: monika.mirkowska@unileoben.ac.at Markus Kratzer, e-mail: markus.kratzer@unileoben.ac.at Christian Teichert, e-mail: christian.teichert@unileoben.ac.at www.unileoben.ac.at/~spmgroup
Contact
[1] M.J. Pearse, M.I. Pope, Powder Technol. 14 (1976) 7 [2] B.A. Kwetkus, Part. Sci. Technol. 16 (1998) 55
[3] D.J. Lacks, Angew. Chem. Int. Ed. 51 (2012) 6822
[4] B.D. Terris, J.E. Stern, D. Rugar, and H.J. Mamin, Phys. Rev. Lett. 63 (1989) 2669 [5] H. Sun, H. Chu, J. Wang, L. Ding, and Y. Li, Appl. Phys. Lett. 96 (2010) 083112
[6] Y.S. Zhou, Y. Liu, G. Zhu, Z.-H. Lin, C. Pan, Q. Jing, and Z.L. Wang, Nano Lett. 13 (2013) 2771 [7] M. Nonnenmacher, M.P. O’Boyle, H.K. Wickramasinghe, Appl. Phys. Lett. 58 (1991) 2921
[8] A. Oberrauner, Dissertation, Chair of Mineral Processing, Montanuniversität Leoben (2011)
Literature
A prototype of the coaxial triboelectrostatic separator[8]
Detailed knowledge about the contact charging of dielectric materials is of great interest for technological applications like tribocharging separation
[1,2]of mineral particles. The underlying mechanisms are still not well understood
[3]. So far, AFM based charging investigations were just performed on dielectric thin layers.
[4-6]Here, an attempt is made to study the electric charging of well-defined surfaces (calcite monocrystals) upon contact with a conductive AFM tip.
Kelvin probe force microscopy (KPFM)
[7]was applied to verify the electrostatic characteristic of the surfaces before and after contact charging. Both, tribocharging due to rubbing and static contact charging with applied tip bias have been investigated.
Motivation
Conclusion
Results
Rubbing
The AFM tip with or without applied bias (0 V or ±10 V) is dragged on a chosen surface area (4 x 4 µm2)with defined force (~3 µN) and speed (0.30 Hz).
Static charging
The AFM tip with applied bias (±10 V)Is brought into contact with a defined force (~2 µN) and for defined time (15 min).
bias -10 V
bias +10 V
x x x x
Before charging
scan size 10 x 10 µm2 each scan took 28 min
Charging: -10 V; 4 times by 15 min
Charge decay after charging (every third scan is shown)
Surface potential [V]
Time [min]
Evolution of the CPD signal with time.
-1,7 -1,2 -0,7 -0,2 0,3
-50 200 450 700 950 1200
average min
max
Time stop: 12 h
before charge decay time stop
charging -10V (12 h)
∆ Surface potential =
∼ -1.5 V
Before charging
scan size 10 x 10 µm2 each scan took 28 min
Charging: -10 V; 4 times by 15 min
Charge decay after charging (every fifth scan is shown)
x x x x
-7 -5 -3 -1 1
-200 0 200 400 600 800
average min
max
Surface potential [V]
Time [min]
Time stop: 14 h
Evolution of the CPD signal with time.
before charging charge decay time stop
-10V (14 h)
∆ Surface potential =
∼ -6.5 V
Evolution of the CPD signal with time.
Time [min]
Surface potential [V]
Before charging
scan size 10 x 10 µm2 each scan took 28 min
Charging: +10 V; 5 times by 15 min
Charge decay after charging (every third scan is shown)
xx x x x x
-0,1 0,9 1,9
-50 450
before charging +10V charge decay
∆ Surface potential =
∼ +2.0 V
x x x x x
Evolution of the CPD signal with time.
2 4 6 8
-200 800 1800
average min
max
Time stop: 18 h 30 min
Surface potential [V]
Time [min]
before charge decay time stop charging +10V (18 h 30 min)
Before charging
scan size 10 x 10 µm2 each scan took 28 min
Charging: +10 V; 5 times by 15 min
Charge decay after charging (every second scan is shown)
∆ Surface potential =
∼ +1.5V
Outlook
Investigation of the influence of parameters like:
• contact force,
• humidity,
• rubbing speed,
• temperature.
Performing contact charging with crystal particle attached to the AFM cantilever.
AFM cantilever
a mineral particle
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