Polymeric surface alteration via scanning probe microscopy

Watson, Jolanta A., Brown, Christopher L., Myhra, Sverre, and Watson, Gregory S. (2006) Polymeric surface alteration via scanning probe microscopy. In: Proceedings of the 2006 International Conference on Nanoscience and Nanotechnology. pp. 592-595. From: ICONN 2006: International Conference on Nanoscience and Nanotechnology, 3-7 July 2006, Brisbane, QLD, Australia.

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This preliminary study focuses on the physical alteration/manipulation of three polymer surfaces (polyimide, PDMS and P(BuMA)), via the scanning probe microscope (SPM). The aim of this study is to investigate the degree of surface manipulation (lithographic outcomes) on the different polymer surfaces under similar raster scanning loading conditions. The polymeric materials were selected based on their varying degree of 'stiffness' (i.e., Young's modulus), commercial availability, potential applications. A clean incompressible silicon surface was used for calibration purposes. Manipulation (particularly on the softer polymer surfaces, PDMS and P(BuMA)) was achieved using stiff levers (i.e., > 4 nNnm-1). The resultant alteration was then analyzed using a soft lever (< 0.1 nNnm -1) to avoid further manipulation and alteration. Lithographic outcomes on a surface are not only dependant on the instrumental parameters (e.g., loading force, orientation and scan speed), but they also depend on the different Young's modulus values of the polymer. It has been demonstrated that at high Young's modulus values (> 5 GPa) no discernable lithographic outcomes have been achieved. At Young's modulus values in the low GPa range (< 2 Gpa), wells, pits and orthogonal grids have be formed. On the other hand, softer polymer surfaces (Young's modulus in the kPa range) induced a stick-slip phenomena.

The stick-slip behaviour was observed in both the slow and fast direction of tip travel and was monitored during the manipulation process via friction loop analysis. After the manipulation process, the area was re-scanned using a soft lever revealing uniformly formed parallel channels. Friction loop analysis revealed a progression of the formation of the stick-slip mechanism in the fast scan direction with the lateral forces gradually increasing as the number of traverses increased. The stick-slip features then begin forming and progressing until the characteristic stick-slip features are observed. Just prior to the probe slipping in the slow scan direction, the stick-slip features in the fast scan direction break down completely. The tip then slips and assumes its next equilibrium position, repeating the cycle.

Lateral force data obtained on all three polymer surfaces and a calibration silicon surface showed the extent of in-plane deformation and frictional variation. The in-plane displacement (i.e., the vertical slope of the friction loop) was found to increase with a decrease in Young’s modulus value which coincides with greater tip trapping, polymer deformation and relaxation. By gradually increasing the loading force, the general trend of the lateral force was observed and plotted. The results are shown in figure 1 below. The lateral force increases linearly with an increase in loading force. As expected, the polyimide and silicon surfaces are comparable due to their Young’s modulus values being > ca. 5 GPa. The P(tBuMA) surface shows a greater increase with the PDMS sample showing the most dramatic increase. The three different linear responses for the PDMS surface are shown for the start, middle and end of a stick-slip cycle, with the final breakdown being omitted. A softer surface will lead to greater tip indentation, higher contact area, and therefore a higher lateral force. At higher loading forces, these effects are amplified.

Item ID: 18219
Item Type: Conference Item (Research - E1)
ISBN: 978-1-4244-0453-7
Keywords: lithography, stick-slip, scanning probe microscopy, manipulation, PDMS, P(tBuMA), polyimide
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Date Deposited: 29 Nov 2017 02:18
FoR Codes: 03 CHEMICAL SCIENCES > 0399 Other Chemical Sciences > 039999 Chemical Sciences not elsewhere classified @ 20%
09 ENGINEERING > 0912 Materials Engineering > 091209 Polymers and Plastics @ 40%
02 PHYSICAL SCIENCES > 0299 Other Physical Sciences > 029904 Synchrotrons; Accelerators; Instruments and Techniques @ 40%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970102 Expanding Knowledge in the Physical Sciences @ 40%
97 EXPANDING KNOWLEDGE > 970103 Expanding Knowledge in the Chemical Sciences @ 20%
97 EXPANDING KNOWLEDGE > 970109 Expanding Knowledge in Engineering @ 40%
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