Combining Fast Imaging and Variable Temperature Studies in Atomic Force Microscopy
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.467
Combining Fast Imaging and Variable Temperature Studies in Atomic Force Microscopy Sergei Magonov1 and Shijie Wu2 1
SPM Labs LLC, Tempe AZ 85283 USA, 2Keysight Technologies, Santa Clara, CA 95051 USA
Abstract
Fast imaging in Atomic Force Microscopy enhances the capability of studying phase transitions and surface properties of materials at variable temperatures. This is demonstrated by measurements of several polymers [poly(diethylsiloxane), low-density polyethylene and ethylene-octene copolymer] and bitumen at low (down to -20˚C) and high (up to +150˚C) temperatures. Monitoring of structural transitions was performed at small and large (up to 40 Pm) areas with 1-5˚C/min cooling/heating rates. Novel data about dynamics and structural transitions of mesomorphic transitions and crystallization were obtained.
INTRODUCTION Atomic force microscopy (AFM) studies at different temperatures enrich our knowledge of structure and properties transformations accompanying thermal transitions in variety of materials. Measurements at high (up to 250˚C) and low temperatures (down to -35˚C) are available with temperature accessories of commercial AFM microscopes. The observations at variable temperatures become more valuable with increased AFM scanning rate that enables fast imaging of small and large areas up to 100 Pm. This is realized by synchronizing a high-speed actuator and a traditional piezo-scanner driven by the same controller with flat frequency response up to 100 kHz. The use of highfrequency probes with resonance above 1 MHz is essential for fast response to tip-sample intermittent contact interaction, which in amplitude modulation mode is defined by Wc = Qc/Sfc with Qc - the quality factor and fc - the probe resonant frequency. Qc is low when operating in water, therefore, fast imaging of biological processes was successfully implemented [1]. Fast imaging at ambient conditions is challenged by high Qc, and it is less developed. Our report brings new insights in this field following an earlier contribution describing high-speed AFM measurements in different environments [2]. In variable temperature studies fast AFM offers substantial time reduction of the experiments and allows monitoring of structural changes induced by temperature change. With high-speed AFM the images can be collected every temperature degree at heating/cooling rates (5-20˚C/min) common for differential scanning calorimetry (DSC). This capability enriches comprehensive material characterization, particularly, for surface structures and thin layers that are not easily accessible by techniques other than AFM. Below we Illustrate fast imaging with variable temperature control using several
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