1. Influence of the mechanical behaviour of cantilevers on the topography of nano-scale grooves during AFM tip-based machining
Raheem Sadoon Jamel1,2 , Emmanuel Brousseau1 , Feodor M. Borodich1
1Cardiff School of Engineering, Cardiff University, Cardiff, United Kingdom
2Department of Mechanical Engineering, Kufa University, Iraq
Contact
Introduction
Experimental Methodology
Results and Discussions
AFM tip-based nanomachining is a method, which may be used to generate micro- and nanoscale cavities on the surface of a processed workpiece [1, 2]. The existing body of research studies in this field demonstrated the implementation this technique along different processing directions. Figure 1 illustrates two of the main machining directions, which are typically found in the literature. For the so-called “forward direction” [3], it is generally assumed, such as in [4-6], that the bending of the cantilever is concave as represented with Figure 1(b). However, the deformed shape of the cantilever along this direction, and also along a direction at an inclined angle with respect to such a pure forward configuration, should depend on load conditions acting on the tip.
A schematic description of the AFM set-up utilised for nanomachining is showed in Figure ‎2. An XE-100 AFM instrument from Park Systems was employed in all experiments. The tests were performed on a single crystal copper sample using a DNISP probe from Bruker. A data acquisition system was developed to capture three voltage signals as described in Table 1. The cutting speed and length of the produced grooves were 5 μm/s and 15 μm, respectively. The machining tests were conducted along the inclined forward direction as specified in Figure 3. The normal loads applied by the tip onto the sample ranged between 14 µN and 40 µN. Fn Fc Mc Z1 V2 V1
STEP3: Steady state machining (keeping the A-B voltage constant) Z2
Backward Direction
STEP 2: Z scanner moving up to reduce the PSPD voltage from V2 to V1
STEP 1: A-B voltage increasing from V1 to V2 as a result of the generation of the moment Mc 2
Convex bending
Y stage motion 
(a) Top view
Backward
Forward
Sample
Directions of motion for the AFM probe:
Cantilever
Forward direction
Cantilever (concave deflection)
(b) Side view
Figure 1. Illustration of backward and forward AFM scratching y x z
Stage
DAQ
PSPD
Mirror
Laser
Controller
Sample
Z scanner A C B D
Inclined Forward Direction
CASE A: Applied force between (14 to 30 µN) Z1 V1 V2 Mc
CASE B: Applied force between (33 to 39 µN) Z2 Z3
Convex
Concave 3
STEP2:The Z scanner moves down increases the voltage
STEP 1: A-B voltage reducing
STEP3:Steady state machining 
STEP4:TheZ-scanner moves down again(deflected shape changed)  
Deflected shape (convex only)
Aim of the research
Figure 2. Schematic description of the
AFM probe-based nano
machining set-up.
The aim of this work is to demonstrate experimentally that both deformed shapes of the cantilever can be observed during actual nanomachining tests along an inclined forward direction depending of the processing conditions utilised as specified in Figure 3.
Table 1 Monitored signals
Name
Physical description
A-B signal
position sensitive photodiode (PSPD).
Z-detector signal
a strain gauge sensor.
Y stage signal
monitoring of the lateral motion of the AFM stage. Y X
Pure forward direction
Inclined forward direction
22.5˚
Tip
Cantilever
Figure 3. Considered inclined forward cutting direction
with respect to the cantilever orientation and
tip geometry.
Illustration of Z-Detector Signal
The groove depth and width increased by over 50% after the cantilever shape change
SEM and AFM inspections of produced grooves
Inclined forward direction
Set normal load: 33 µN
Cutting direction
2 µm
200 nm
Selected cross sections 4
Shearing
Ploughing V0 A
Tip approach
stage Z1 B
Indentation stage Z2 C
Transition stage D
Scratching stage E
Tip retraction stage
V1 (corresponding to a set applied force) or
Material to be removed 1 2 3 4
AFM nanomachining stages 1
References
Conclusions
[1] Tseng A 2011 Small
[2] Yan Y, Geng Y and Hu Z 2015 Int. J. Mach. Tools Manuf
[3] Tseng A, et al .J 2011 Appl. Surf. Sci
[4] Ruan J-A and Bhushan B 1994 Journal of Tribology
[5] Malekian M, et al J. Micromech. and Microeng (11pp)
[6] Geng Y, et al J. Vac. Sci. Technol. B
The deflection of the probe may change from a convex to a concave shape during the actual groove formation process.
2. This phenomenon during machining significantly influences the
resulting groove topography
3. It is important to take into account the non-rigid nature of AFM probes
when studying AFM tip-based nanomachining.