Nondestructive Characterization of a Polymer Nanocoating using WITec Alpha300 AR - Application Note by WITec

Topics Covered

Background
Introduction
Combination of Non-destructive Measuring Methods in Alpha300 AR
Topography Images of Polymer Films Recorded with AFM
High Resolution AC Mode AFM Images of Polymer Blend
Alpha300 AR Spectral Imaging Mode Operations

Background

WITec is a manufacturer of high-performance instrumentation for scientific and industrial applications focused on new solutions for Optical and Scanning Probe Microscopy.

Introduction

Characterization of heterogeneous systems on the nanometer scale continues to grow in importance and to impact key applications in the field of materials science (phase segregated systems), nanotechnology (molecular electronics), and catalysis (single site catalysts). Detailed information on this scale is necessary to test and evaluate advanced materials. Certain properties, however, are difficult to study with conventional characterization techniques due to the inability of these methods to chemically differentiate materials with sufficient spatial resolution, without damage, staining or preferential solvent washing.

Combination of Non-destructive Measuring Methods in Alpha300 AR

The "alpha300 AR" combines two non-destructive measuring methods: the high spatial resolution of an AFM with the chemical identification capabilities of the Confocal Raman Microscope. To demonstrate the advantage of this unique combination, thin films of polymers have been studied.

Topography Images of Polymer Films Recorded with AFM

Fig. 1 shows the topography image of a 100 nm thick PMMA film spin coated on a glass cover slip and fig. 2 shows the high resolution phase image of a SBR film, both recorded with the AFM. Fig. 3 and fig. 4 show the corresponding Raman spectra.

Figure 1. AFM topography image of a PMMA film.

Figure 2. AFM phase image of a SBR film.

 

Figure 3. Raman spectrum of PMMA.

Figure 4. Raman spectrum of SBR.

In figure 2, an overview AFM image of a PMMA-SBR blend is presented. The topographic image reveals round features, 20-30 nm in height with a diameter varying from 150 nm to 4 µm. To determine the height of the PMMA-SBR film, the polymer was scratched off with a fine needle and imaged with the AFM again as shown in figure 6.

Figure 5. Overview AFM image of a PMMA-SBR blend.

Figure 6. AFM Image of the scratched PMMA-SBR film.

The cross-section (fig. 7) marked with a black line in the AFM image indicates that the low areas of the polymer blend are 30 nm in height, whereas the higher round features are up to 70 nm high.

Figure 7. Graph of the cross-section at the black line in Fig. 6 through the film.

High Resolution AC Mode AFM Images of Polymer Blend

Figs. 8a+b show a high resolution AC Mode AFM image of the polymer blend. The 2x2 µm topographical image reveals the 20 nm high round features. The simultaneously recorded phase image shows the fine structure, observed in the plain SBR film, in the lower part of the topographical image, whereas the higher features do not reveal any fine texture in the phase image.

Based on these high resolution images, a correlation of the two polymers in the blend is already possible, the higher features representing the PMMA and the lower features the SBR. It is not yet clear if the SBR forms a uniform film on the glass substrate and the higher islands of PMMA are formed on top of the SBR film, or if both phases reach the glass substrate. The answer to this question can only be provided by a spectroscopic method.

The relative wave numbers of the individual Raman spectra of the PMMA and SBR indicate that the positions of the characteristic peaks and their intensities can be used to distinguish the two polymers if blended.

Alpha300 AR Spectral Imaging Mode Operations

Operating the "alpha300 AR" in spectral imaging mode, a complete Raman spectrum is collected at every image pixel. The measured spectra were fit to the Raman spectrum of PMMA and SBR as shown in fig. 3 and fig. 4 to distinguish the polymers as illustrated in figs. 9 +10. Comparing the Raman data to the AFM images, it is clear, that the higher round features are PMMA down to the glass substrate, whereas the 30 nm high background represents the SBR phase.

Figures 8a+b. High resolution AFM images of the polymer blend PMMA-SBR spin-coated on a glass cover slip. Topography (left) and phase (right). Scan size: 2 µm x 2 µm.

Figure 9. Color coded Raman image of SBR resulting from the integral intensity of each spectrum.

Figure 10. Color coded Raman image of PMMA resulting from the integral intensity of each spectrum.

Figure 11. Corresponding spectra: SBR (blue) and PMMA (red).

Source: Characterization of the Polymer Blend PMMA-SBR Combining Confocal Raman and Atomic Force Microscopy - Application Note by Witec. 

For more information on this source please visit Witec

Date Added: Nov 7, 2007 | Updated: Sep 18, 2013
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