Current Opportunities and Challenges in Biopolymer Thin Film Analysis—Determination of Film Thickness

Abstract

Polymer thin films with thickness below 100 nm are a fascinating class of 2D materials with commercial and research applications in many branches ranging from coatings to photoresists and insulating materials, to mention just a few uses. Biopolymers have extended the scope of polymer thin films with unique materials such as cellulose, cellulose nanocrystals, cellulose nanofibrils with tunable water uptake, crystallinity and optical properties. The key information needed in thin biopolymer film use and research is film thickness. It is often challenging to determine precisely and hence several techniques and their combinations are used. Additional challenges with hydrophilic biopolymers such as cellulose are the presence of humidity and the soft and often heterogenous structure of the films. This minireview summarizes currently used methods and techniques for biopolymer thin film thickness analysis and outlines challenges for accurate and reproducible characterization. Cellulose is chosen as the representative biopolymer.

Thickness measurement of thin films using atomic force microscopy based scratching

“…Thickness is a fundamental property of such films with a significant influence on their physical properties [1]. Most common methods for film thickness measurement are spectroscopic techniques such as ellipsometry, reflectometry and x-ray reflectivity, or microscopic techniques such as scanning electron microscopy and transmission electron microscopy, profilometry and atomic force microscopy (AFM) [2][3][4]. The choice of the most suitable measurement method is not a straightforward task since it depends on many factors such as film morphology (film thickness, surface roughness, underlying substrate, etc.…”

Thickness Determination and Control in Protein-Based Biomaterial Thin Films

“…Similarly, in AFM, a nanoscale tip probes the surface topography of samples with nanometer resolution. AFM has been widely applied to the local characterization of the thickness and roughness of organic films and biomaterial assemblies. − Finally, other techniques, such as surface plasmon resonance (SPR) measurements have also been applied to quantify the thickness of biomaterial films …”