Chris Murray

Relative humidity control for atomic force microscopes

We describe the design and performance of a relative humidity (RH) control chamber for use with atomic force microscopes (AFM) in which the tip is scanned across the stationary sample. The small volume (∼9cm3) chamber encloses the sample, the cantilever holder, and a commercial humidity/temperature sensor. The RH is controlled by passing a controlled ratio of dry and humid nitrogen gas across the sample. This unique design prevents exposure of the scanner assembly to humid gas and maintains all of the functionalities of the AFM system with no measurable degradation of its performance. Using this system, the RH at the sample position can be varied between 5% and 95% and controlled to within ±0.2% during an AFM measurement. To demonstrate the performance of the RH control chamber in imaging and force spectroscopy modes, we have characterized the RH-dependent swelling of small chitosan droplets with diameters of 3–40μm, and the RH dependence of capillary forces between the AFM tip and a mica surface.

A novel integrated system for analysis of thermal depth profiles

In this work a novel system for the study of thermal profiles and time dependent heat diffusion is presented. In this system the modulation of light is made directly using an electronic driver that turns on and off the laser diode. The data acquisition is made with a higher accuracy than in the conventional systems because the electronics that detects the signal is the one that generates the modulating signal. The system is very compact and as a consequence, shows a higher stability, and can be integrated in systems in which other measurements are performed or inside of chambers where the conditions of the surroundings are controlled. In order to show the potential of our system, applications using photoacoustic and photopyroelectric techniques are presented. In the case of photoacoustics, the specific case of the open photoacoustic cell for thermal diffusion characterization is shown. Using a conventional photoacoustic cell, it is shown that the dynamics of evaporation and crosslinking can be followed in polymers. In the case of photopyroelectric technique, thermal depth profiles are also performed and the study of dynamics a as function of time is discussed. The advantages of our system and the different modes of detection are discussed.